Hello Elvin.D,

               It depends on what platform you want to work. You may go for CCNA(Cisco Certified Network Associate) will give a vast knowledge of networking , MCSE(Microsoft Cerfied System Engineer) will make you proficient with Windows Client Server architecture, although I would recommend you to get some basic networking ideas or pursue a course on Network+ Certification. There are other certifications but these will build your foundation on networking. 

Regards

Prantik 

Wide Area Network:WANs are used to connect LANs and other types of networks together irrespective of geographical boundaries.

The Internet can be considered as an example of WAN- in respect to the huge geographical area it covers.

Application layer

Routing is the process of forwarding IP packets from one network to another. A router is a device that joins networks together and routes traffic between them. A router will have at least two network cards (NICs), one physically connected to one network and the other physically connected to another network. A router can connect any number of networks together providing it has a dedicated NIC for each network.

The router takes your computer’s local IP address out of the packet’s Source Address and puts it in a table. It then puts the external IP into the packets Source Address space. The router also copies the Destination Address IP from the packet and puts it in the table associated with your local IP.

Install a Network Printer on Your Home or Office Network

Step 1: First, connect the printer to your network by connecting one end of a Cat 5 or 6 cable (which should have come with your printer) to your router and the other end into the network port of your printer. Now, turn your printer on and wait for it to become ready.

Step 2: Next you’ll need to get the IP address of your printer. The IP address is what will let your computer know where to find your printer on the network. All network printers allow you to print a configuration sheet that will list basic information about the printer along with the current network configuration.

For most printers, this involves pressing the Menu button on the printer, going to theInformation option and choosing Print Configuration. Sometimes if there is no display, you just press and hold the Go or Print button down for about 10 seconds and it’ll print the configuration page. You will be looking for the TCP/IP section:

The IP Address is what you’ll need for the next steps. You printer should automatically get an IP address from the DHCP server on your network. At home, the IP should be coming from the wireless router or residential gateway if you have one that acts as a cable modem plus router.

Step 3: The last step is to add the printer to your computer. Click on Start, then Printers and Faxes.If you don’t see this in your Start Menu, you can go to Start, Control Panel and then click on Printers and Faxes there. Click Add Printer from the task pane on the left.

The Add Printer wizard will begin, so click Next to get started. On the next screen you’ll be asked whether your printer is a local printer or a network printer. These options are confusing because a network printer is actually referring either a printer connected to another computer or a printer on a print server. Our printer is a stand-alone printer and so you must select Local printer attached to this computer and make sure that you uncheckthe box for automatically detecting the printer.

Click Next and you’ll be asked to select the printer port. Since our printer is a network printer with a IP address, we need to select the Create a new port option and chooseStandard TCP/IP Port.

Click Next and you’ll get another wizard to add a TCP/IP printer port. On the main wizard screen click Next. In the first text box, Printer Name or IP Address, enter the IP address from the printer configuration sheet you printer earlier.

Click Next and depending on the printer you have, you may get one more dialogs before the end of the wizard. If the network card for the printer cannot be identified, the wizard will ask you to choose the card type. You can leave the default of “Generic Network Card” and click Next.

Click Next and click Finish. You will then continue on with the Add Printer wizard and you’ll need to either choose the printer from the list of manufacturers or click Have Disk and insert your printer driver cd in the computer.

Click Next and enter a name for your printer and click the Yes radio button if you would like the printer to be your default printer.

Click Next and you’ll be asked whether you want to share the printer or not. Click No because anyone else who wants to connect will be able to do so following the same steps. In later versions of Windows XP, the printer sharing dialog has been removed. Click Next and click Yes to print a test page and make sure that the computer and printer can communicate!

Click Next and then click Finish! The new printer will appear in your Printers and Faxes screen and you’re ready to print to your network printer.

Hub supports up to 10 mbps and switch supports up to 10/100/1000 mbps.

The main difference between hubs and switches is the bandwidth available to network users.

If your network consists of very few nodes, a hub may be the best way to go. However, always keep in mind future expansion of the network. If bandwidth could become an issue among the users of the network, using a switch will increase the efficiency of the network.

Remember that you do not necessarily have to choose between hubs and switches. Your network may benefit most from a combination of the two, with critical components directly connected to the switch, and non-critical components on a hub connected to the switch.

An encoder is a circuit that changes a set of signals into a code. In digital electronics it encodes(converts or compress) more inputs to less outputs. Ex: a 2-to-1 line encoder(D1 and D0 will give output A=0 when D1=1 and D2=0).It actually has four inputs therefore one question we need to answer is what to do with those other inputs? Do we ignore them? Do we have them generate an additional error output? In many circuits this problem is solved by adding sequential logic in order to know not just what input is active but also which order the inputs became active.

There are two ways to pass arguments/parameters to function calls -- call by value andcall by reference. The major difference between call by value and call by reference is that in call by value a copy of actual arguments is passed to respective formal arguments. While, in call by reference the location (address) of actual arguments is passed to formal arguments, hence any change made to formal arguments will also reflect in actual arguments.

Ex: Suppose you want to edit an image. There are two methods to do so : Method 1 : If you want to keep the original image as well as the edited image. What you'll do is make a copy of the image, modify it and save it. This is call by value method -  You make a copy of the actual parameters, perform operations on those copies but do not modify the actual parameters. Method 2 : If you want to modify the original image permanently. What you'll do is acces the image from its location (reference), modify it and save it. This is call by reference - you use references to access the actual parameters, perform operations on those parameters using those references and hence end up modifying the actual parameters.

Boolean Algebra: The most obvious way to simplify Boolean expressions is to manipulate them in the same way as normal algebraic expressions are manipulated. With regards to logic relations in digital forms, a set of rules for symbolic manipulation is needed in order to solve for the unknowns.

A set of rules formulated by the English mathematician George Boole describe certain propositions whose outcome would be either true or false. With regard to digital logic, these rules are used to describe circuits whose state can be either, 1 (true) or 0 (false). In order to fully understand this, the relation between the AND gate, OR gate and NOT gate operations should be appreciated. A number of rules can be derived from these relations. Here is an example table to demonstrate:

P1: X = 0 or X = 1  P2: 0 . 0 = 0  P3: 1 + 1 = 1  P4: 0 + 0 = 0  P5: 1 . 1 = 1  P6: 1 . 0 = 0 . 1 = 0  P7: 1 + 0 = 0 + 1 = 1 

There are different laws for boolean algebra. Every law has two expressions, (a) and (b). This is known as duality. These are obtained by changing every AND(.) to OR(+), every OR(+) to AND(.) and all 1's to 0's and vice-versa. It has become conventional to drop the dot(.) AND symbol, i.e. A.B is written as AB.

A LAN is typically something completely within your own premises (your organization's campus, or building, or office suite, or your home), so it's something you build and own yourself, all the way down to the physical cabling. In contrast, a WAN is something that connects between geographically separated locations, so you generally have to lease access to lines or data transmission services from telecommunications carriers to create your WAN.

Because of the shorter distances needed for on-premises networks, and because of the focus on connecting PCs and servers, LANs tend to be built on Ethernet and other 802.3-family (and 802.11-family) physical layers and data links. 1000BASE-T, 1000BASE-SX, 1000BASE-LX, etc.

Because off-premises network links usually need to go longer distances and work over the telecommunication carriers' existing infrastructure, they tend to use physical and data-link standards that are more common in the telecom industry. Then again, for your convenience, telecom carriers usually hand off to you using an 802.3-family link, even if what they're using behind the scenes is.

Because of the technical hurdles associated with moving lots of data long distances reliably, WAN links tend to be lower bandwidth and higher latency than LAN links. Also, because you're usually paying a separate telecom carrier for the service, to keep costs down, most organizations try to limit (or at least not go crazy with) how much data they move over WAN links.

The differences between LANs and WANs tend to be at the physical and data-link layers. At the network layer (Layer 3 in the old-but-still-helpful-for-some-discussions OSI layering model), most people use IP (Internet Protocol) nowadays. Because it all uses IP, applications that use IP don't have to know what physical and data-link layers are in use, so anything you can do on a LAN you can potentially do on a WAN as well, if you have high enough bandwidth and low enough latency for whatever it is you're trying to do, and as long as you haven't blocked it at your firewall (or via the accidentally firewall-like properties of a NAT).

Logic Gates: Digital systems are said to be constructed by using three basic logic gates. These gates are the AND gate, OR gate and NOT gate.

Boolean functions may be practically implemented by using electronic gates. The following points are important to understand.

Electronic gates require a power supply. Gate INPUTS are driven by voltages having two nominal values, e.g. 0V and 5V representing logic 0 and logic 1 respectively. The OUTPUT of a gate provides two nominal values of voltage only, e.g. 0V and 5V representing logic 0 and logic 1 respectively. There is always a time delay between an input being applied and the output responding. 

1: The AND gate is an electronic circuit that gives a high output(1) if all its inputs are high. A dot (.) is used to show the AND operation. Bear in mind that this dot is usually omitted.

2: The OR gate is an electronic circuit that gives a high output if one or more of its inputs are high(1). A plus (+) is used to describe the OR operations.

3: The NOT gate is an electronic circuit that produces an inverted version of the inputs logic at its output. It is also known as an inverter. If the input variable is A, the inverted output is known as NOT A.

URLs Uniform Resource Locator occur most commonly to reference web pages (http), but are also used for file transfer (ftp), email (mailto), database access (JDBC), and many other applications.

The Anatomy of a URL: Although each URL is a single string of numbers, letters, and special characters, each URL has four distinct components:

• Protocol — always present
• Hostname — always present
• Path or Stem — always present…but sometimes is, basically, null
• Parameters — optional (but this is where some of the real fun can happen)

The Internet is the largest Wide Area Network, spanning the Earth.

Control Program

Software that controls the operation of a computer and has highest priority.A program which carries on input/output operations, loading of programs, detection of errors, communication with the operator, and so forth. Operating Systems are the primary example.

A computer system has many resources – hardware & software that may be required to solve a problem, like CPU time, memory space, file-storage space, I/O devices & so on. The Operating System(OS) acts as a manager for these resources so it is viewed as a resource allocator.

The OS is viewed as a control program because it manages the execution of user programs to prevent errors & improper use of the computer.

Computer hardware is the physical parts or components of a computer, such as the monitor, mouse, keyboard, computer data storage, hard disk drive (HDD), system unit (graphic cards, sound cards, memory, motherboard and chips), and so on, all which are physical objects that can be touched (that is, they are tangible).

For typical desktop computers, the processor, main memory, secondary memory, power supply, and supporting hardware are housed in a metal case. Many of the components are connected to the main circuit board of the computer, called the motherboard.

A bridge, or network bridge, is a device that can also connect networks, but unlike a router, its operation does not include the network layer of the OSI model. A bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or Token Ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street.

A router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination.The third layer, which is the network layer of the OSI model, is where routers operate. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway (where one network meets another), including each point-of-presence on the Internet. A router is often included as part of a network switch.Router determines the fastest way possible, which is also usually the shortest way possible, in a particular network. It has the capability to route the packets through the most effective determined route.

Points to remember:

1. Routers are more intelligent than bridges.

2. Routers allow hosts that aren’t practically on the same logical network to be able to communicate with each other, while bridges can only connect networks that are logically the same.

3. Routers operate at the layer 3 (network layer) of the OSI model, while bridges are only at the layer 2 (Data link layer).

4. Routers understand and consider IP and IPX addresses, while bridges do not, and instead they recognize MAC addresses.

5. Routing is more efficient, and has better call management, than bridging.

Higher carrying capacity - Because optical fibers are comparatively thinner, more fibres can be bundled into a given-diameter cable. This allows more lines to go over the same cable or more channels to come through the cable into your end device, much greater bandwidth.

Light signals - Unlike electrical signals, light signals from one fiber do not interfere with those of other fibres in the same cable. This means clearer communication or reception of signals.Because optical fibre transmits light (photons) rather than electrons, it does not radiate electromagnetic fields, nor is it susceptible to electromagnetic fields. Thus, optical fibre transmissions do not suffer from cross talk, electrically noisy environments, or electromagnetic interference problems.

A computer can process data, pictures, sound and graphics. They can solve highly complicated problems quickly and accurately. A computer performs basically five major computer operations or functions irrespective of their size and make. These are 1) it accepts data or instructions by way of input, 2) it stores data, 3) it can process data as required by the user, 4) it gives results in the form of output, and 5) it controls all operations inside a computer.

Almost from its creation, email has been the most widely used Internet application, and in that respect can claim to be the most important. These same capabilities also underlie the technology of mailing lists. The following sections describe the key features of email.

• Email Is One-To-Many
• Email Is Almost Free.

An operating system or OS is a software on the hard drive that enables the computer hardware to communicate and operate with the computer software. Without an operating system, a computer and software programs would be useless. It is like an interpreter between user and hardware.

The operating system's tasks, in the most general sense, are;

•  Processor management
•  Memory management
• Device management
• Storage management
• Application Interface 
•  User Interface

Hubs operate(specified) at Layer 1 (Physical Layer) of the OSI model.

A hub sends data packets (frames) to all devices on a network, regardless of any MAC addresses contained in the data packet.

The show ip interface command is used to determine if an IP access list is enabled on a particular interface.

Router# show ip interface

UDP:User Datagram Protocol is used, and it is a connection network service at the Transport layer, and DHCP uses this connectionless service.

Application layer protocols uses the services provided by the lower layers (in this case UDP, transport layer) to transmit their data. Another way of saying this: DHCP is a service. UDP is the protocol carrying this service.

Call by Value

If data is passed by value, the data is copied from the variable used in for example main() to a variable used by the function. So if the data passed (that is stored in the function variable) is modified inside the function, the value is only changed in the variable used inside the function.

Call by Reference

If data is passed by reference, a pointer(C) / reference to an object (an alias for the original object)(c++), to the data is copied instead of the actual variable as is done in a call by value. Because a pointer is copied, if the value at that pointers address is changed in the function, the value is also changed in main().

Basic or Fundamental Datatypes in C++ are

• Character denoted by char is the data type that holds an integral value corresponding to the representation of an element of the ASCII character set.
• Integer denoted by int is the data type that holds an integer value or a whole number.
• Real denoted by:
  • float is the data type that holds a single–precision floating point value or a real number; or
  • double is the data type that holds a double–precision floating point value or a real number.
• Boolean denoted by bool is the data type that holds a boolean value of true or false.

In GUI interfaces, the taskbar is a desktop toolbar application that lets you perform tasks such as switching between open windows and starting new applications.It is movable, concealable icon bar that is set on the very edge of the graphical user interface (GUI) desktop and serves as a launching pad for applications as well as a holder for icons indicating running programs.The taskbar is usually associated with the Microsoft Windows interface.

The taskbar is the thin strip that runs across the bottom of your screen. It is split into a number of different areas: a round Start button, Quick Launch icons, a notification area, and a clock. All other areas are the Taskbar itself.

The taskbar was first introduced by Microsoft in Windows 95 and has since been adopted by other operating systems. Although other desktop environments like Linux’s KDE Plasma and GNOME have their own taskbars, the most popular taskbar is the one in the Microsoft Windows operating systems.

Standard and extended access control lists (ACLs) are two main types which are used to configure security on a router.

You need to specify the name or number of the ACL and the direction in which the router will filter information:

• in? As traffic enters the interface of the router from the network segment

• out? As traffic leaves the interface to the network segment

Backing Up Router Configuration(IOS)

To copy the configuration from the router to the TFTP server you can use the copy run tftp command. It will backup the router configuration thats stored in DRAM. Then you will be asked to enter the address of the TFTP server and the name of the destination file on TFTP server like this:

[Router name] #copy run tftp -- to copy the running configuration to TFTP server

Address or name of remote host []? 172.16.10.2 -- the ip address of TFTP server

Destination filename [routername-confg]? /Backup/Router01.cfg -- the folder path on the server where the configuration file will be stored)

There are many ways to get copy of the configuration by TFTP, FTP server or by network software tools

If we are going to use TFTP server we have to do that below configuration after download and install tftp server software:

copy running-config startup-config

or

R1#copy running-config tftp:

Address or name of remote host []?10.1.3.250

Destination filename [R1-confg]? backup_cfg_for_my_router

!!

1030 bytes copied in2.489 secs (395 bytes/sec)

R1#

Integrated Services Digital Network (ISDN): ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of most people's complete communications needs at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. Ex:phone line you use to get on to the internet. Asynchronous Transfer Mode (ATM): is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ATM provides data link layer services that run over Layer 1 links. This differs from other technologies based on packet-switched networks (such as the Internet Protocol or Ethernet), in which variable sized packets (known as frames when referencing layer 2) are used. ATM is a connection-oriented technology, in which a logical connection is established between the two endpoints before the actual data exchange begins. Ex: machine you get money out of.

Data structure refers to a scheme for organizing data, or in other words a data structure is an arrangement of data in computer's memory in such a way that it could make the data quickly available to the processor for required calculations. A data structure should be seen as a logical concept that must address two fundamental concerns. First, how the data will be stored, and second, what operations will be performed on it? As data structure is a scheme for data organization so the functional definition of a data structure should be independent of its implementation. The functional definition of a data structure is known as ADT (Abstract Data Type) which is independent of implementation. The implementation part is left on developers who decide which technology better suits to their project needs.

Data structures can be broadly classified in two categories - linear structures and hierarchical structures. Arrays, linked lists, stacks, and queues are linear structures, while trees, graphs, heaps etc. are hierarchical structures. Every data structure has its own strengths, and weaknesses. Also, every data structure specially suits to specific problem types depending upon the operations performed and the data organization. For example, an array is suitable for read operations.

Canonical forms express all binary variables in every product (AND) or sum (OR) term of the Boolean function. There are two types of canonical forms of a Boolean expression. The first one is called sum of products or “SoP“  and the second one is called product of sums or “PoS”. A’BC+A’BC’+ABC’+AB’C’+A’B’C’+ABC is a canonical sum of product form of a Boolean function, the given function has contained three inputs that means three binary variables. In each term of the given function has contained three variables.  (X’+Y+Z).(X+Y’+Z).(X’+Y+Z).(X’+Y+Z’) is a canonical product of sum form of a Boolean function.

Generally, firewalls examine all the data packets passing through them to see if they meet the rules defined by the ACL (Access Control List) made by the administrator of the network. Only if the Data Packets are allowed as per ACL, they will be transmitted over the Connection.

Firewalls also maintain a log of Important Activities inside the Network. A Network Administrator can define what is important for him and configure the Firewall to make the Logs accordingly. Firewall can filter contents on the basis of Address, Protocols, Packet attributes, State, and it’s generally only Screen the Packet Headers.

Types of Firewalls

• Packet Filtering Firewalls
• Circuit level gateways firewalls
• Application level gateways firewalls
• Stateful multilayer Inspection Firewall

General benefits

A good broadband connection to your home means there's a greater capacity to send and receive data. It means that data be received and sent far more quickly to and from your computer. This allows you to access the Internet, browse the web more effectively, download files faster and send and receive emails quicker.

• A broadband connection is "always on" - no waiting for dial-up connectivity if you still use this route to the Internet. This means that you are immediately more productive without having to wait for a connection.
• As broadband comes at a fixed price, you can budget effectively.
• Many websites are now "media-rich". This means that they don't just have text and limited graphics, but have interactive elements, streaming sound and video and other elements. They are designed to be used via broadband.

Share your broadband connection

With a high speed broadband connection, you can easily share a connection to the Internet amongst several PCs or other devices in your home. Most Broadband routers have wireless connectivity; you can use this for computers, mobile phone, Tablet PC’s and many games consoles. 

Many homes now have several PC's, laptops, and other devices (such as Nintendo Wii's, Smart Phones and even e-book readers such as the Amazon Kindle) that can access the Internet. By setting up a simple Wi-Fi (wireless) network in your home, all family members will be able to access the Internet via a range of devices. This means that employment, education, leisure and entertainment possibilities are open to all the family.

Madurai Institute of Engineering and Technology

K.L.N. College Of Engineering 

Sacs M.A.V.M.M. Engineering College 

Thiagarajar College of Engineering 

Velammal College of Engineering and Technology

A stack is a restricted data structure, because only a small number of operations are performed on it. Elements are removed from the stack in the reverse order to the order of their addition.

Application of Stack :

• Parsing
• Recursive Function
• Calling Function
• Expression Evaluation

           Expression Conversion

• Infix to Postfix
• Infix to Prefix
• Postfix to Infix
• Prefix to Infix

​​Towers of hanoi

A[2] means the  element at third position of an array as the index usually starts from 0 ex:-A[n].

*A[2] refers to the element at third position as it dereferences the address and gives us the value.

Remote Desktop Protocol (RDP) is a secure network communications protocol for Windows-based applications running on a server.

RDP allows network administrators to remotely diagnose and resolve problems encountered by individual subscribers. RDP is available for most versions of theWindows operating system as well as Mac OS X. An open source version is also available.

The rlogin and rsh commands for remote login and remote execution of commands are inherited from UNIX. While seldom used because they are blatantly insecure, they still come with almost every Linux distribution for backward compatibility with UNIX programs.

Telnet, on the other hand, is still commonly used, often by system and network administrators. Telnet is one of the most powerful tools for remote access to files and remote administration, allowing connections from anywhere on the Internet. Combined with an X server, remote graphical applications can be displayed locally. There is no difference between working on the local machine and using the remote machine.

There are two major differences.

A non-member(Ordinary) function always appears outside of a class.The member function can appear outside of the class body (for instance, in the implementation file). But, when you do this, the member function must be qualified by the name of its class. This is to identify that that function is a member of a particular class.

For instance, if you took our myarray class and wanted to define the implementation of a new member function called myfunction outside the body of the class.

You would write:

int myarray::myfunction(int a, int b) { ...//details of this implementation //note: you need the protype of myfunction in the body of myarray }

The myarray:: specifies that the myfunction belongs to the myarray class.

By contrast, a non-member function has no need to be qualified. It does not belong to a class. In the implementation file, I could write my non-member function as:

int myfunction (int a, int b) { ..//details of this implementation }

Another difference between member functions and non-member functions is how they are called (or invoked) in the main routine. Consider the following segment of code:

int main() { int i; myarray a; //declare a myarray object i=myfunction(3,2); //invoking the non-member function i=a.myfunction(3,2); //invoking the member function }

EDI is a standardized method for transferring data between different computer systems or computer networks. It is commonly used fore-commerce purposes, such as sending orders to warehouses, tracking shipments, and creating invoices.

Because may online retailers sell products that they do not physically stock, it is important to have an easy way to transfer order information to the locations where the goods are stored. EDI makes this possible. Some common EDI formats include X12 (U.S.), TRADACOMS (U.K.), and EDIFACT (International).

What exactly is compilation?

In a compiled implementation of a language, a compiler will translate the program directly into code that is specific to the target machine, which is also known as machine code – basically code that is specific to a given processor and operating system. Then the computer will run the machine code on its own.

What exactly is interpretation?

In an interpreted implementation of a language, the source code is not directly run by the target machine. What happens instead is that another program reads and then executes the original source code. This other program is also known as the interpreter. The interpreter is usually written specifically for the native machine. As an example, you could consider the multiplier operation – the “*”. If the interpreter sees this in your code, then at run time it would call its own definition of the multiplier function – maybe something called “multiply(x,y)”. And then that “multiply(x,y)” would execute the machine code’s equivalent of the multiply instruction.

In interpretation, the original source code is also typically converted into some intermediate code which is then processed by an interpreter that converts the intermediate code into machine specific code.

Robotics is the study of robots. Robots are machines that can be used to do jobs. Some robots can do work by themselves. Other robots must always have a person telling them what to do.

Roboticists develop man-made mechanical devices that can move by themselves, whose motion must be modelled, planned, sensed, actuated and controlled, and whose motion behaviour can be influenced by “programming”. Robots are called “intelligent” if they succeed in moving in safe interaction with an unstructured environment, while autonomously achieving their specified tasks.

This definition implies that a device can only be called a “robot” if it contains a movable mechanism, influenced by sensing, planning, actuation and control components. It does not imply that a minimum number of these components must be implemented in software, or be changeable by the “consumer” who uses the device; for example, the motion behaviour can have been hard-wired into the device by the manufacturer.

1.Degree. This is the number of entities involved in the relationship and it is usually 2 (binary relationship) however Unary and higher degree relationships can be exists. 2.Cardinality. This specifies the number of each entity that is involved in the relationship there are 3 types of cardinality for binary relationships one to one (1:1) one to many (1:n) many to many (n:m)

When an object goes out of scope or is deleted, the sequence of events in its complete destruction is as follows: The class's destructor is called, and the body of the destructor function is executed. Destructors for nonstatic member objects are called in the reverse order in which they appear in the class declaration.

• Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse.

• Abstraction is the concept of hiding irrelevant details.In other words make complex system simple by hiding the unnecessary detail from the user.

It is one of the great discoveries of programming that you can write any program using just simple while loops and if statements. You don't need any other control statements at all. Of course it might be nice to include some other types of control statement to make life easy - for example, you don't need the for loop, but it is good to have! So as long as you understand the if and the while loop in one form or another you can write any program you want to.

If you think that a loop and an if statement are not much to build programs then you are missing an important point. It's not just the statements you have, but the way you can put them together. You can include an if statement within a loop, loops within loops are also OK, as are loops in ifs, and ifs in ifs and so on. This putting one control statement inside another is called nesting and it is really what allows you to make a program as complicated as you like.

Yet another research area in AI, neural networks, is inspired from the natural neural network of human nervous system.

What are Artificial Neural Networks (ANNs)?

The inventor of the first neurocomputer, Dr. Robert Hecht-Nielsen, defines a neural network as −

"...a computing system made up of a number of simple, highly interconnected processing elements, which process information by their dynamic state response to external inputs.”

Basic Structure of ANNs

The idea of ANNs is based on the belief that working of human brain by making the right connections, can be imitated using silicon and wires as living neuronsand dendrites.

The human brain is composed of 100 billion nerve cells called neurons. They are connected to other thousand cells by Axons. Stimuli from external environment or inputs from sensory organs are accepted by dendrites. These inputs create electric impulses, which quickly travel through the neural network. A neuron can then send the message to other neuron to handle the issue or does not send it forward.

ANNs are composed of multiple nodes, which imitate biological neurons of human brain. The neurons are connected by links and they interact with each other. The nodes can take input data and perform simple operations on the data. The result of these operations is passed to other neurons. The output at each node is called its activation or node value.

Each link is associated with weight. ANNs are capable of learning, which takes place by altering weight values.

Expert system, a computer program that uses artificial-intelligencemethods to solve problems within a specialized domain that ordinarily requires human expertise.

Expert system applications

Here are some uses for an expert system

• Diagnostic tool for fixing machinery and vehicles
• Online medical system for diagnosing a problem
• Telephone based help desk
• Finance firm making loan / credit decisions
• Government services such as working out tax and benefits

In each case, the expert system is designed to provide a reasonable answer with some systems also giving a reason for each answer.

A good example of an online expert system is the very popular NHS direct web site that provides sensible advice on common medical symptoms

Components of an Expert System

An expert system has 3 components:

The Knowledge Base - Where the information is stored in the expert system in the form of facts and rules (basically a series of IF statements). This is where the programmer writes the code for the expert system.

The User Interface - Where the user interacts with the expert system. In other words where questions are asked, and advice is produced. As well as the advice that is output, the user interface can output the justification features of an expert system. This is either How justification - where the system justifies its reasoning for providing a piece of advice or Why justification - where the system justifies why a particular question is being asked. Justification allows the user piece of mind about why a question is asked or a piece of advice is provided, and can increase their confidence in taking such advice.  It also makes it easier for the programmer of the system to ensure that it works correctly as it will flag up areas where the expert system provides advice that is not intended by the programmer.

Inference Engine - This applies the facts to the rules and determines the questions to be asked of the user in the user interface and in which order to ask them. This is the 'invisible' part of the expert system, which is active during a consultaion of the system (when the user chooses to run the program).

An expert system has 3 components:

The Knowledge Base - Where the information is stored in the expert system in the form of facts and rules (basically a series of IF statements). This is where the programmer writes the code for the expert system.

The User Interface - Where the user interacts with the expert system. In other words where questions are asked, and advice is produced. As well as the advice that is output, the user interface can output the justification features of an expert system. This is either How justification - where the system justifies its reasoning for providing a piece of advice or Why justification - where the system justifies why a particular question is being asked. Justification allows the user piece of mind about why a question is asked or a piece of advice is provided, and can increase their confidence in taking such advice.  It also makes it easier for the programmer of the system to ensure that it works correctly as it will flag up areas where the expert system provides advice that is not intended by the programmer.

Inference Engine - This applies the facts to the rules and determines the questions to be asked of the user in the user interface and in which order to ask them. This is the 'invisible' part of the expert system, which is active during a consultaion of the system (when the user chooses to run the program).

In artificial intelligence, an expert system is a computer system that emulates the decision-making ability of a human expert. Expert systems are designed to solve complex problems by reasoning about knowledge, represented primarily as if–then rules rather than through conventional procedural code.

Artificial intelligence, or AI, is the field that studies the synthesis and analysis of computational agents that act intelligently. Let us examine each part of this definition.

An agent is something that acts in an environment - it does something. Agents include worms, dogs, thermostats, airplanes, robots, humans, companies, and countries.

We are interested in what an agent does; that is, how it acts. We judge an agent by its actions.

An agent acts intelligently when

• what it does is appropriate for its circumstances and its goals,
• it is flexible to changing environments and changing goals,
• it learns from experience, and
• it makes appropriate choices given its perceptual and computational limitations. An agent typically cannot observe the state of the world directly; it has only a finite memory and it does not have unlimited time to act.

A computational agent is an agent whose decisions about its actions can be explained in terms of computation. That is, the decision can be broken down into primitive operation that can be implemented in a physical device. This computation can take many forms. In humans this computation is carried out in "wetware"; in computers it is carried out in "hardware." Although there are some agents that are arguably not computational, such as the wind and rain eroding a landscape, it is an open question whether all intelligent agents are computational.

The central scientific goal of AI is to understand the principles that make intelligent behavior possible in natural or artificial systems. This is done by

• the analysis of natural and artificial agents;
• formulating and testing hypotheses about what it takes to construct intelligent agents; and
• designing, building, and experimenting with computational systems that perform tasks commonly viewed as requiring intelligence.

As part of science, researchers build empirical systems to test hypotheses or to explore the space of possibilities. These are quite distinct from applications that are built to be useful for an application domain.

Note that the definition is not for intelligent thought. We are only interested in thinking intelligently insofar as it leads to better performance. The role of thought is to affect action.

The central engineering goal of AI is the design and synthesis of useful, intelligent artifacts. We actually want to build agents that act intelligently. Such agents are useful in many applications.

Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols.

IPv6, addresses are expressed as a series of eight 4-character hexadecimal numbers, which represent 16 bits each (for a total of 128 bits).

An example would be:

3ffe:1900:4545:3:200:f8ff:fe21:67cf

Colons separate 16-bit fields. Leading zeros can be omitted in each field as can be seen above where the field :0003: is written :3:. In addition, a double colon (::) can be used once in an address to replace multiple fields of zeros. For example:

fe80:0:0:0:200:f8ff:fe21:67cf

can be written

fe80::200:f8ff:fe21:67cf

Hardware is a comprehensive term for all of the physical parts of a computer, as distinguished from the data it contains or operates on, and the software that provides instructions for the hardware to acoomplish tasks. The boundary between hardware and software is slightly blurry - firmware is software that is "built-in" to the hardware, but such firmware is usually the province of computer programmers and computer engineers in any case and not an issue that computer users need to concern themselves with.

A typical computer (Personal Computer, PC) contains in a desktop or tower case the following parts:

• Motherboard which holds the CPU, main memory and other parts, and has slots for expansion cards
• power supply - a case that holds a transformer, voltage control and fan
• storage controllers, of IDE, SCSI or other type, that control hard disk , floppy disk, CD-ROM and other drives; the controllers sit directly on the motherboard (on-board) or on expansion cards
• graphics controller that produces the output for the monitor
• the hard disk, floppy disk and other drives for mass storage
• interface controllers (parallel, serial, USB, Firewire) to connect the computer to external peripheral devices such as printers or scanners

External hardware examples

• Flat-panel, Monitor, and LCD
• Keyboard
• Microphone
• Mouse
• Printer
• Projector
• Scanner
• Speakers
• USB thumb drive

Internal hardware examples

• CPU
• Drive (e.g. Blu-Ray, CD-ROM, DVD, floppy drive, and hard drive)
• Fan (heat sink)
• Modem
• Motherboard
• Network card
• RAM
• Sound card
• Video card

An operating system or OS is a software program that enables the computer hardware to communicate and operate with the computer software. Without a computer operating system, a computer and software programs would be useless.

• An operating system is a program that acts as an interface between the software and the computer hardware.

• It is an integrated set of specialised programs that are used to manage overall resources and operations of the computer.

• It is specialised software that controls and monitors the execution of all other programs that reside in the computer, including application programs and other system software.

A file is a collection of records which have common properties. Each file has its own file reference which is unique. The file reference indicates the subject or contexts of the records.

A record can be an image, text based or in electronic or physical format.

Physical address is used in main memory. Logical address is used in virtual memory. Logical and physical addresses are same in compile time and load time but differ in execution time address binding scheme.

Logical: An address generated by CPU is referred to us a logical address. The set of all logical address generated by a program is a logical address space. For user view. The user program deals with logical address or these are generated by user (program). 

Physical: An address seen by memory unit that is, the one loaded into the memory address register of the memory is referred to as physical address. The set of all physical address corresponding to these logical addresses is a physical address. For system view. These are generated by memory management unit (MMU).

The 5 most important and commonly used network topologies are as follows: Bus topology

Star topology

Ring topology

Tree topology

Mesh topology

Star topology is the most popular network topology in businesses today. It consists of nodes connected to a central switch or hub. If you have a home network, you are probably using the star topology. Bustopology is one which consists of all of the workstations connected to a single cable.

Another popular topology used these days are Hybrid networks provide a lot of flexibility, and as a result, they have become the most widely used type of topology. Common examples are star ring networks and star bus networks. Tree topology is one specific example of a star bus network

Management of I/O devices is a very important part of the operating system - so important and so varied that entire I/O subsystems are devoted to its operation. ( Consider the range of devices on a modern computer, from mice, keyboards, disk drives, display adapters, USB devices, network connections, audio I/O, printers, special devices for the handicapped, and many special-purpose peripherals. )

I/O Subsystems must contend with two ( conflicting? ) trends: (1) The gravitation towards standard interfaces for a wide range of devices, making it easier to add newly developed devices to existing systems, and (2) the development of entirely new types of devices, for which the existing standard interfaces are not always easy to apply.

Device drivers are modules that can be plugged into an OS to handle a particular device or category of similar devices.

• I/O devices can be roughly categorized as storage, communications, user-interface, and other
• Devices communicate with the computer via signals sent over wires or through the air.
• Devices connect with the computer via ports, e.g. a serial or parallel port.
• A common set of wires connecting multiple devices is termed a bus.
  • Buses include rigid protocols for the types of messages that can be sent across the bus and the procedures for resolving contention issues.
  •  three of the four bus types commonly found in a modern PC:

    The PCI bus connects high-speed high-bandwidth devices to the memory subsystem ( and the CPU. )

    The expansion bus connects slower low-bandwidth devices, which typically deliver data one character at a time ( with buffering. )

    The SCSI bus connects a number of SCSI devices to a common SCSI controller.

    A daisy-chain bus, ( not shown) is when a string of devices is connected to each other like beads on a chain, and only one of the devices is directly connected to the host.

The NAND gate and the NOR gate can be said to be universal gates since combinations of them can be used to accomplish any of the basic operationsand can thus produce an inverter, an OR gate or an AND gate. The non-inverting gates do not have this versatility since they can't produce an invert.

NAND and NOR Gates are called Universal Gates because all the other gates can be created by using these gates

Examples: 

NOR AS NOT This is made by joining the inputs of a NOR gate. As a NOR gate is equivalent to an OR gate leading to NOT gate, this automatically sees to the "OR" part of the NOR gate, eliminating it from consideration and leaving only the NOT part.

NOR AS OR The OR gate is simply a NOR gate followed by a NOT gate. NOR AS AND An AND gate gives a 1 output when both inputs are 1; a NOR gate gives a 1 output only when both inputs are 0. Therefore, an AND gate is made by inverting the inputs to a NOR gate. NOR AS NAND A NAND gate is made using an AND gate in series with a NOT gate.

In propositional logic and boolean algebra, De Morgan's laws are a pair of transformation rules that are both valid rules of inference. They are named after Augustus De Morgan, a 19th-century British mathematician. The rules allow the expression ofconjunctions and disjunctions purely in terms of each other via negation.

We have known the basic operation of binary arithmetic such as binary addition, binary subtraction, binary multiplication and binary division. Now we will look through the most important part of binary arithmetic on which a lot of Boolean algebra stands, that is De-Morgan's Theorem which is called De-Morgan's Laws often.

Before discussing De-Morgan's theorems we should know about complements. Complements are the reverse value of the existing value. We are trying to say that as there are only two digits in binary number system 0 & 1. Now if A = 0 then complement of A will be 1 or A’ = 1

De Morgan’s theorem can be stated as follows:- Theorem 1: The compliment of the product of two variables is equal to the sum of the compliment of each variable. Thus according to De-Morgan's laws or De-Morgan's theorem if A and B are the two variables or Boolean numbers. Then accordingly (A.B)’ = A’ + B’ Theorem 2: The compliment of the sum of two variables is equal to the product of the compliment of each variable. Thus according to De Morgan’s theorem if A and B are the two variables then. (A + B)’ = A’.B’

When dissolved in fluid, salts tend to break apart into their component ions, creating an electrically-conductive solution. For example, table salt (NaCl) dissolved in water dissociates into its component positive ion of sodium (Na+) and negative ion of chloride (Cl-). Any fluid that conducts electricity, such as this new saltwater solution, is known as an electrolyte solution: the salt ions of which it’s composed are then commonly referred to as electrolytes.

Prior to the early 1920's, chemists doubted the existence of molecules having molecular weights greater than a few thousand. This limiting view was challenged by Hermann Staudinger, a German chemist with experience in studying natural compounds such as rubber and cellulose. In contrast to the prevailing rationalization of these substances as aggregates of small molecules, Staudinger proposed they were made up of macromolecules composed of 10,000 or more atoms. He formulated a polymeric structure for rubber, based on a repeating isoprene unit (referred to as a monomer). For his contributions to chemistry, Staudinger received the 1953 Nobel Prize. The terms polymer and monomer were derived from the Greek roots poly (many), mono (one) and meros (part).

Recognition that polymeric macromolecules make up many important natural materials was followed by the creation of synthetic analogs having a variety of properties. Indeed, applications of these materials as fibers, flexible films, adhesives, resistant paints and tough but light solids have transformed modern society. Some important examples of these substances are discussed in the following sections.

In data communication, a node is any active, physical, electronic device attached to anetwork. These devices are capable of either sending, receiving, or forwarding information; sometimes a combination of the three. There are many examples of nodes ranging from bridges, switches, hubs and modems to other computers, printers, andservers. One of the most common forms of a node is a host computer; often referred to as an Internet node.

Network topology refers to the physical or logical layout of a network. It defines the way different nodes are placed and interconnected with each other. Alternately, network topology may describe how the data is transferred between these nodes.

There are two types of network topologies: physical and logical. Physical topology emphasizes the physical layout of the connected devices and nodes, while the logical topology focuses on the pattern of data transfer between network nodes.

The physical and logical network topologies of a network do not necessarily have to be identical. However, both physical and network topologies can be categorized into five basic models:

• Bus Topology: All the devices/nodes are connected sequentially to the same backbone or transmission line. This is a simple, low-cost topology, but its single point of failure presents a risk.
• Star Topology: All the nodes in the network are connected to a central device like a hub or switch via cables. Failure of individual nodes or cables does not necessarily create downtime in the network but the failure of a central device can. This topology is the most preferred and popular model.
• Ring Topology: All network devices are connected sequentially to a backbone as in bus topology except that the backbone ends at the starting node, forming a ring. Ring topology shares many of bus topology's disadvantages so its use is limited to networks that demand high throughput.
• Tree Topology: A root node is connected to two or more sub-level nodes, which themselves are connected hierarchically to sub-level nodes. Physically, the tree topology is similar to bus and star topologies; the network backbone may have a bus topology, while the low-level nodes connect using star topology.
• Mesh Topology: The topology in each node is directly connected to some or all the other nodes present in the network. This redundancy makes the network highly fault tolerant but the escalated costs may limit this topology to highly critical networks.

The name modem means modulator demodulator. A modem connects our computer to a standard phone line or to our cable, which allows us to send data or receive data. A modem is a conversion device that converts signals from one device into signals another device can read. For example, a modem may covert the digital data of a computer into an analog signal that can be read and carried by a telephone line. The modulator part of the modem converts digital signals to analog signals, and the demodulator part converts analog signals to digital signals.

Modems use two different forms of data transmission: synchronous and asynchronous. Synchronous transmission uses timing signals, and asynchronous uses error-correcting formulas in its transmission. Modems can use one form of transmission or the other, or they can use both.

The functions of modems have changed over the years; first they were used for telegrams and to transmit data for American air defense in the 1950s. Modems were used with computers for the first time in 1977 to transmit data between computers. In the beginning uses of modems and computers, data only circulated among a small amount of computers in the same vicinity while being controlled by a host computer. As modems improved and were able to transmit information faster, data was able to be transmitted between more hosts, and the Internet network slowly spread.

The four types of modems are the fax modem, which solely transfers data between fax machines, the traditional ISDN modem, the Digital Subscriber Line and the cable modem

Bandwidth is a broad term defined as the bit-rate measure of the transmission capacity over a network communication system. Bandwidth is also described as the carrying capacity of a channel or the data transfer speed of that channel. However, broadly defined, bandwidth is the capacity of a network. Bandwidth exists in physical or wireless communication networks.

Data is sent over a network from a source and is received by a node at its destination. Imagine that each side of the transmission has a modem with a different data rate. For example, the modem on the source side might be 256 Kbps, while the modem on the destination side is capable for 128 Kpbs. This will not be a good combination for efficient communication as both ends have different data transfer rates, which ultimately causes delays in communication.

LAN:

A local area network (LAN) is a computer network within a small geographical area such as a home, school, computer laboratory, office building or group of buildings.

A LAN is composed of inter-connected workstations and personal computers which are each capable of accessing and sharing data and devices, such as printers, scanners and data storage devices, anywhere on the LAN. LANs are characterized by higher communication and data transfer rates and the lack of any need for leased communication lines.

In the 1960s, large colleges and universities had the first local area networks (LAN). In the mid-1970s, Ethernet was developed by Xerox PARC (Xerox Palo Alto Research Center) and deployed in 1976. Chase Manhattan Bank in New York had the first commercial use of a LAN in December 1977. In the late 1970s and early 1980s, it was common to have tens or hundreds of individual computers located in the same site. Many users and administrators were attracted to the concept of multiple computers sharing expensive disk space and laser printers.

From the mid 1980s to through the 1990s, Novell's Netware dominated the LAN software market. Over time, competitors such as Microsoft came out with comparable products to the point where nowadays, local networking is considered base functionality for any operating system. example:Small Home Office

WAN:A wide area network (WAN) is a network that exists over a large-scale geographical area. A WAN connects different smaller networks, including local area networks (LAN) and metro area networks (MAN). This ensures that computers and users in one location can communicate with computers and users in other locations. WAN implementation can be done either with the help of the public transmission system or a private network.

A WAN connects more than one LAN and is used for larger geographical areas. WANs are similar to a banking system, where hundreds of branches in different cities are connected with each other in order to share their official data.

A WAN works in a similar fashion to a LAN, just on a larger scale. Typically, TCP/IP is the protocol used for a WAN in combination with devices such as routers, switches, firewalls and modems. example:Internet

Networking is required to make accessible communication between computers possible by a network connection. Networking allows for many possibilities, such as accessing the internet, file sharing, file transferring, networks attacks and system communication.

Types of Networks:

LAN(Local Area Networking)

WLAN(Wireless Local Area Networks)

WAN(Wide Area Networks)

MAN(Metropolitan Area Networks)

CAN(Campus Area Networks)

SAN(Storage or Sytem Area Network)

PAN(Personal Area Network)

Dan(Desk Area Network)

Twisted pair - Wire twisted to avoid crosstalk interference. It may be shielded or unshielded.

• UTP-Unshielded Twisted Pair. Normally UTP contains 8 wires or 4 pair. 100 meter maximum length. 4-100 Mbps speed.
• STP-Shielded twisted pair. 100 meter maximum length. 16-155 Mbps speed. Lower electrical interference than UTP.

Coaxial - Two conductors separated by insulation such as TV 75 ohm cable. Maximum length of 185 to 500 meters.

• Thinnet - Thinnet uses a British Naval Connector (BNC) on each end. Thinnet is part of the RG-58 family of cable*. Maximum cable length is 185 meters. Transmission speed is 10Mbps. Thinnet cable should have 50 ohms impedance and its terminator has 50 ohms impedance. A T or barrel connector will have no impedance. Maximum thinnet nodes are 30 on a segment. One end of each cable is grounded.
• Thicknet - Half inch rigid cable. Maximum cable length is 500 meters. Transmission speed is 10Mbps. Expensive and is not commonly used. (RG-11 or RG-8). A vampire tap or piercing tap is used with a transceiver attached to connect computers to the cable. 100 connections may be made. The computer has an attachment unit interface (AUI) on its network card which is a 15 pin DB-15 connector. The computer is connected to the transceiver at the cable from its AUI on its network card using a drop cable. Maximum thicknet nodes are 100 on a segment. One end of each cable is grounded.

Fiber-optic - Data is transmitted using light rather than electrons. Usually there are two fibers, one for each direction. Cable length of 2 Kilometers. Speed from 100Mbps to 2Gbps. This is the most expensive and most difficult to install, but is not subject to interference. Two types of cables are: Single mode cables for use with lasers has greater bandwidth and costs more. Injection laser diodes (ILD) work with single mode cable. Multimode cables for use with Light Emitting Diode (LED) drivers. All signals appear to arrive at the same time. P intrinsic N diodes or photodiodes are used to convert light to electric signals when using multimode.

A path through which information is transmitted from one place to another is called communication channel. It is also referred to as communication medium or link. The twisted pair wire, coaxial cable, fiber optic cable,Radio Broadcast, Cellular Radio, microwave, satellite etc. are examples of communication channels.

A path through which information is transmitted from one place to another is called communication channel. It is also referred to as communication medium or link

In computing, a server is a computer program or a device that provides functionality for other programs or devices, called "clients". This architecture is called the client–server model, and a single overall computation is distributed across multiple processes or devices.

Computers required on a network can be broadly grouped according to the following roles:

• Server roles – servers can be configured to perform a number of roles. The applications that the server is running specify the particular server’s role. Servers typically need services and additional features installed to perform its specific role. When compared to workstations, servers have more disk space and memory and faster processors. The server’s role determines the hardware that servers require. A few common server roles are listed below:
  • Domain controller
  • Database server
  • Backup server
  • File server
  • Print server
  • Infrastructure server
  • Web server
  • E-mail server
• Desktop workstation roles – desktop workstations differ from servers in that desktop workstations are general purpose computers that can perform a number of functions.
• Portable workstation roles – portable workstations are the solution to bringing a desktop computer’s features to an off-site employee.

Windows Server 2003 introduced the concept of server roles. Server roles basically group related administrative tasks and provide a specific capability or function for the network design. With Windows Server 2003, if a server is configured for a certain server role, then a number of additional services, features, and tools are installed for the server. In this manner, the server is set up to provide users with the required services.

Windows Server 2003 provides a new tool for defining and managing server roles, namely, the Manage Your Server utility. The actual Wizard for applying the server roles to computers is the Configure Your Server Wizard. The Configure Your Server Wizard is included within the Manage Your Server utility and is also managed through this utility.

For Windows Server 2003, there are 11 different server roles that can be configured with the Configure Your Server Wizard:

• File server
• Print server
• Application server
• Mail server
• Terminal server
• Remote access server/VPN server
• Domain controllers
• DNS server
• WINS server
• DHCP server
• Streaming media server

A collection of computers and other devices that are connected together by communication channels for sharing information and resources is called computer network. The resources may include printers, scanners, and hard disks etc. Computer network is also called the information network. The most popular information network is the Internet. In a computer network, two important technologies: computing and telecommunication work together.

The main benefits or uses of computer network are:

• Communication
• Sharing Resources
• Sharing Software
• Data Sharing

Applications of logic topology networks.

• Bus topology: Ethernet uses the logical bus topology to transfer data. Under a bus topology a node broadcasts the data to the entire network. All other nodes on the network hear the data and check if the data is intended for them.
• Ring topology: In this topology, only one node can be allowed to transfer the data in a network at a given time. This mechanism is achieved by token (the node having token only can transmit the data in a network) and hence the collision can be avoided in a network.

Pair Reduction Rule : Remove the variable which changes its state from complemented to uncomplemented or vice versa.Pair removes one variable only.

Quad Reduction Rule : Remove the two variables which change their states.A quad removes two variables.

Octet Reduction Rule : Remove the three variables which changes their state.Octet removes three variables.

Full Adder. The full-adder circuit adds three one-bit binary numbers (C A B) and outputs two one-bit binary numbers, a sum (S) and a carry (C1). The full-adder is usually a component in a cascade of adders, which add 8, 16, 32, etc. binary numbers.

The half adder is an example of a simple, functional digital circuit built from two logic gates. The half adder adds to one-bit binary numbers (AB). The output is the sum of the two bits (S) and the carry (C). Note how the same two inputs are directed to two different gates.

The Karnaugh map, also known as the K-map. Maurice Karnaugh introduced it in 1953 as a refinement of Edward Veitch's 1952 Veitch diagram.

Principle of Duality

"1+1=01+1=0" is a statement (a boolean statement), and indeed, 1+1=11+1=1 happens to be a true statement.

Likewise, the entire statement "0⋅0=00⋅0=0" is a true statement, since 0⋅00⋅0 correctly evaluates to false: and this is exactly what "0⋅0=00⋅0=0" asserts, so it is a correct (true) statement about the falsity of 0⋅00⋅0

The duality principle ensures that "if we exchange every symbol by its dual in a formula, we get the dual result".

As well as a standard Boolean Expression, the input and output information of any Logic Gate or circuit can be plotted into a standard table to give a visual representation of the switching function of the system. The table used to represent the boolean expression of a logic gate function is commonly called a Truth Table. A logic gate truth table shows each possible input combination to the gate or circuit with the resultant output depending upon the combination of these input(s).

For example, consider a single 2-input logic circuit with input variables labelled as A and B. There are “four” possible input combinations or 22 of “OFF” and “ON” for the two inputs. However, when dealing with Boolean expressions and especially logic gate truth tables, we do not general use “ON” or “OFF” but instead give them bit values which represent a logic level “1” or a logic level “0” respectively.

Then the four possible combinations of A and B for a 2-input logic gate is given as:

• Input Combination 1. – “OFF” – “OFF” or ( 0, 0 )
• Input Combination 2. – “OFF” – “ON” or ( 0, 1 )
• Input Combination 3. – “ON” – “OFF” or ( 1, 0 )
• Input Combination 4. – “ON” – “ON” or ( 1, 1 )

Therefore, a 3-input logic circuit would have 8 possible input combinations or 23 and a 4-input logic circuit would have 16 or 24, and so on as the number of inputs increases. Then a logic circuit with“n” number of inputs would have 2n possible input combinations of both “OFF” and “ON”.

So in order to keep things simple to understand, in this tutorial we will only deal with standard 2-input type logic gates, but the principals are still the same for gates with more than two inputs.

A logic gate is an elementary building block of a digital circuit. Mostlogic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels.

A logic gate might sound horribly complex, but it's simply an electric circuit with two inputs and an output. It receives two incoming electric currents, compares them, and sends on a new, outgoing electric current depending on what it finds. A logic gate is a bit like a doorman or bouncer who is allowed to let people into a nightclub only if they pass certain tests. There are quite a few different types of logic gate, the most common of which are called AND, OR, NOT, XOR (Exclusive Or), NAND (NOT AND), and NOR (NOT OR)

A tautology is sort of like circular logic compressed into one statement, so that the statement is technically true, but still meaningless. Tautologies are a key concept in propositional logic, where a tautology is defined as a propositional formula that is true under any possible Boolean valuation of its propositional variables.

Fallacies of definition are the various ways in which definitions can fail to explain terms. efers to the concept of making an error in terms of reasoning. It is crucial to understand logical fallacies so that they can be identified and avoided when attempting to persuade.

Data

Think of data as a "raw material" - it needs to be processed before it can be turned into something useful. Hence the need for "data processing". Data comes in many forms - numbers, words, symbols. Data relates to transactions, events and facts. On its own - it is not very useful.

Information

Information is data that has been processed in such a way as to be meaningful to the person who receives it. Businesses and other organisations need information for many purposes.

UK mathematician and computer pioneer George Boole (1815-65) developed boolean algebra.

Algorithm and Flowchart

To cope with a problem we need to make a better plan which will be convinent and easy to solve that particular problem. It is not that we cannot tackle with that problen but the thing is that we may not be successful. So, in computer programming  too we need to plan before designing any problem. Algorithm and flowchart are the two basic terms which aids for the development  of a software package conveniently.

ALGORITHM

An algorithm is a step wise set of finite instructions written to solve a problem. It will be easier to code a program after we can have well prepared algorithm and flowchart. An algorithm is written on simple language and must be efficient and limited  to finite number of steps.

FLOWCHART

Flowchart is the diagrammatic representation of an algorithm with the help of symbols carryig certain meaning. Using flowchart, we can easily understand a porogram. Flowchart is not language specific. We can use the same  flowchart to code a program using different programming languages. Though desingning a flowchart helps the coding easier, the designing of flowchart is not a simple task and is time consuming.

For a function that does not return anything. Basically all the computation are done within the function and you've nothing to return the caller, the void keyword specifies that the function does not return a value. When used for a function's parameter list, void specifies that the function takes no parameters. When used in the declaration of a pointer, void specifies that the pointer is "universal."

Types of Operating Systems

Batch operating system

The users of batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. Thus, the programmers left their programs with the operator. The operator then sorts programs into batches with similar requirements.

The problems with Batch Systems are following.

• Lack of interaction between the user and job.

• CPU is often idle, because the speeds of the mechanical I/O devices is slower than CPU.

• Difficult to provide the desired priority.

Time-sharing operating systems

Time sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed as time-sharing. The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of Multiprogrammed batch systems, objective is to maximize processor use, whereas in Time-Sharing Systems objective is to minimize response time.

Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently. Thus, the user can receives an immediate response. For example, in a transaction processing, processor execute each user program in a short burst or quantum of computation. That is if n users are present, each user can get time quantum. When the user submits the command, the response time is in few seconds at most.

Operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time. Computer systems that were designed primarily as batch systems have been modified to time-sharing systems.

Advantages of Timesharing operating systems are following

• Provide advantage of quick response.

• Avoids duplication of software.

• Reduces CPU idle time.

Disadvantages of Timesharing operating systems are following.

• Problem of reliability.

• Question of security and integrity of user programs and data.

• Problem of data communication.

Distributed operating System

Distributed systems use multiple central processors to serve multiple real time application and multiple users. Data processing jobs are distributed among the processors accordingly to which one can perform each job most efficiently.

The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines). These are referred as loosely coupled systems or distributed systems. Processors in a distributed system may vary in size and function. These processors are referred as sites, nodes, computers and so on.

The advantages of distributed systems are following.

• With resource sharing facility user at one site may be able to use the resources available at another.

• Speedup the exchange of data with one another via electronic mail.

• If one site fails in a distributed system, the remaining sites can potentially continue operating.

• Better service to the customers.

• Reduction of the load on the host computer.

• Reduction of delays in data processing.

Network operating System

Network Operating System runs on a server and and provides server the capability to manage data, users, groups, security, applications, and other networking functions. The primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks. Examples of network operating systems are Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.

The advantages of network operating systems are following.

• Centralized servers are highly stable.

• Security is server managed.

• Upgrades to new technologies and hardwares can be easily integrated into the system.

• Remote access to servers is possible from different locations and types of systems.

The disadvantages of network operating systems are following.

• High cost of buying and running a server.

• Dependency on a central location for most operations.

• Regular maintenance and updates are required.

Real Time operating System

Real time system is defines as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. Real time processing is always on line whereas on line system need not be real time. The time taken by the system to respond to an input and display of required updated information is termed as response time. So in this method response time is very less as compared to the online processing.

Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application. Real-time operating system has well-defined, fixed time constraints otherwise system will fail.For example Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, and home-applicance controllers, Air traffic control system etc.

There are two types of real-time operating systems.

Hard real-time systems

Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems secondary storage is limited or missing with data stored in ROM. In these systems virtual memory is almost never found.

Soft real-time systems

Soft real time systems are less restrictive. Critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems.For example, Multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers etc.

Types of databases

a) Operational databases

b) End user databases

c) Centralised databases

d) Distributed databases

e) Personal databases

f) Commercial databases

a. Operational databases:

These databases store data relating to the operations of the enterprise. Generally, such databases are organised on functional lines such as marketing, production, employees, etc.

b. End-User databases:

These databases are shared by users and contain information meant for use by the end-users like managers at different levels. These managers may not be concerned about the individual transactions as found in operational databases.

Rather, they would be more interested in summary information. Although, the operational databases can also generate summary information from the transaction details, they would be quite slow as they are not designed for this purpose.

c. Centralised databases:

These databases store the entire informa­tion and application programs at a central computing facility. The users at different locations access the central data base to make processing. The communication controller sends the transactions to the relevant application programs. These programs pick up the appropriate data from the database for processing the transaction.

For example, Mahanagar Telephone Nigam Limited (MTNL) has a centralised data base for registration of applications for new tel­ephone connections. The data regarding the applicant are received from a local area office of MTNL.

Data validation and verification is carried out by the application programs at the central computer centre, and a registration number is allotted by the application pro­grams located at the central facility. The local area office keeps on recording it and hardly does any processing.

d. Distributed databases:

These databases have contributions from the common databases as well as the data captured from the local operations. The data remains distributed at various sites in the organisation. As the sites are linked to each other with the help of communication links, the entire collection of data at all the sites constitutes the logical database of the organisation.

These data­bases reduce the communication requirement by ensuring that the detailed local information remains stored on the local facility. To­day, the client-server technology is most popular for managing distributed data bases. In a client-server environment, DBMS has two components, one interacting with the needs of the user (client) and passing requests to the other component of DBMS.

The other component interacts with the database to meet the information needs of the client. Figure 9.8 depicts the functioning of these components of DBMS in a client server environment.

The basic reason for dividing the DBMS into two components is that a part of the job is moved to the user’s PC (client). This makes the simultaneous processing possible on client PC and Server com­puter system. The server is also able to co-ordinate the requests from a number of clients at a time.

e. Personal databases:

The personal databases are maintained, gen­erally, on Personal computers. They contain information that is meant for use only among a limited number of users, generally working in the same department.

These databases are generally subject specific and are user designed. They use simple and less powerful DBMS packages available on PCs. These DBMS packages may not have all the features of relational DBMS but do have simi­lar features in a limited way.

f. Commercial databases:

The database to which access is provided to users as a commercial venture is called a commercial or external database. These databases contain information that external users would require but by themselves would not be able to afford main­taining such huge databases.

These databases are subjected specific and access to these databases is sold as a paid service to its user. There are many commercial database services available, particularly in the area of financial and technical information.

These databases may offer statistics regarding commodity, foreign exchange and stock markets, companies and their performance, importers and their buy­ing patterns, decided case laws, etc. The access to commercial databases may be given through communication links.

Some of the database service providers also offer databases on CD-ROMs and the updated versions of the databases are made available periodically. The databases on CD-ROMs have the advantage of reduced cost of communication. However, in applications such as stock market, com­modity market and currency market information, this medium is not suitable because information is needed on a ‘real-time’ basis.

Page stealer finds the page eligible for swapping and places the page number in the list of pages to be swapped. Kernel copies the page to a swap device when necessary and clears the valid bit in the page table entry, decrements the pfdata reference count, and places the pfdata table entry at the end of the free list if its reference count is 0.

BASIC POSTULATES OF BOOLEAN ALGEBRA

• If X = 0 then X = 1 and if X = 1 then X = 0

• Logical addition (OR relations)

•  0+0=0
•  0+1=1
•  1+0=1
•  1+1=1

• Logical multiplication (AND relations)

• 0.0=0
• 0.1=0
• 1.0=0
• 1.1=1

• Complement rules (NOT relations)

• 0’ = 1
• 1’ = 0

Logical functions test for a condition to evaluate it as true or false, Logical functions can also evaluate parameters such as text or arithmetic operations that do not make a true or false statement. While each logical element or condition must always have a logic value of either "0" or "1", we also need to have ways to combine different logical signals or conditions to provide a logical result.

Some basic logical functions are:

AND:The AND gate implements the AND function. With the gate shown to the left, both inputs must have logic 1 signals applied to them in order for the output to be a logic 1. With either input at logic 0, the output will be held to logic 0. 

OR:The OR gate is sort of the reverse of the AND gate. The OR function, like its verbal counterpart, allows the output to be true (logic 1) if any one or more of its inputs are true. 

NOT:The inverter is a little different from AND and OR gates in that it always has exactly one input as well as one output. Whatever logical state is applied to the input, the opposite state will appear at the output.

Page-Stealer is created by the Kernel at the system initialization and invokes it throughout the lifetime of the system. Kernel locks a region when a process faults on a page in the region, so that page stealercannot steal the page, which is being faulted in.

During the fork() system call the Kernel makes a copy of the parent process’s address space and attaches it to the child process. But the vfork() system call do not makes any copy of the parent’s address space, so it is faster than the fork() system call. The child process as a result of the vfork() system call executes exec() system call. The child process from vfork() system call executes in the parent’s address space (this can overwrite the parent’s data and stack ) which suspends the parent process until the child process exits.

Shell is a UNIX term for the interactive user interface with an operating system. The shell is the layer of programming that understands and executes the commands a user enters. In some systems, the shell is called a command interpreter. A Unix shell is what gives Unix its powerful capabilities. The shell is the part of the system with which the user interacts, and as such it is arguably the most important part of a Unix system. A Unix shell interprets commands such as(think of the DOS operating system and its "C:>" prompts and user commands such as "dir" and "edit") "pwd", "cd" or "traceroute" and sends the proper instructions to the actual operating system itself. Other functions of a shell include scripting capability, path memory, multitasking, and file handling.

tcsh (/ˌtiːˈsiːʃɛl/ "tee-cee-shell", /ˈtiːʃɛl/ "tee-shell", or as an acronym "tee cee ess aitch") is a Unix shell based on and compatible with the C shell (csh). It is essentially the C shell with programmable command-line completion, command-line editing, and a few other features.

Swapping is the procedure of copying out the entire process(its address space) from main memory to some sort of secondary storage(typically hard disk or tape storage). Usually this is done as a result of CPU scheduling.  Operating System typically maintains a read-to-run queue of processes. The queue comprises of information about processes that are ready for the execution in memory. However, the images of these processes can either be in memory or on disk (in which case it needs to be loaded into memory off the disk). If the process that is to be scheduled next is on disk, and there is no free space in main memory, a process that is currently resident in memory is swapped back to disk. The process that is to be executed next can then be loaded into memory and allocated space for its data segment, text segment etc. The most important thing to note here is that the complete process is swapped in/out. There is no granularity over here as to what part of process's address space is swapped back to disk. The complete process image in its entirety is swapped back to disk. This should be very clear when we are trying to understand the differences between paging and swapping. Paging on the other hand is a memory allocation technique that allows the physical address space of the process to be non-contiguous. In other words, a process can be allocated memory wherever it is available and the unit of allocation is the size of page or frame (usually 4KB , but it is system dependent). Wherever a free frame is available in main memory, a physical page belonging to the process can be loaded into it and the page table of process will take care of mapping the logical address (logical page numbers) to correct physical frames in memory (may or may not be contiguous).  If you are trying to understand the differences or establish some sort of relation between paging and swapping, you would probably want to understand demand paging.Demand Paging is a technique to implement virtual memory. Here, the process is again allocated memory in terms of pages, but the entire process(all of its physical pages) need not exist in the memory for the execution to begin.  As and when the memory references are made for the pages currently not resident in memory, the operating system loads the desired page into memory from the disk and updates the page table of the process. While doing so, it may decide to replace some page which is already in memory. This will create space for the new page that is waiting to be loaded in.   The above paragraph is something you are looking for. In swapping, we understood that a process (in memory) is swapped with another process (on disk). In demand paging, a page (in memory and part of process' address space) is swapped/replaced with another page (on disk, but belongs to the process).  As mentioned in Operating System Concepts (Silberschatz et al.), use of the term swapping is technically incorrect when discussing paging or demand paging. Swapping refers to the manipulation of entire process, where as the latter sees the process as a sequence of pages.

Mount system call makes a directory accessible by attaching a root directory of one file system to another directory. In UNIX directories are represented by a tree structure, and hence mounting would mean attaching them to the branches. This means the file system found on one device can be attached to the tree. The location in the system where the file is attached is called as a mount point. Example:- Mount –t type device dir

- This will attach or mount the file system found on device of type type to the directory dir. - Unmount system calls does the opposite. It un mounts or detaches the attached file front the target or mount point. If a file is opened or used by some process cannot be detached.

The attaching of a file system to another file system is done by using mount system call. At the time of mounting, there is an essential splicing one directory tree onto a branch in another directory tree is done. The mount takes two arguments. One – the mount point, which is a directory in the current file naming system, two – the file system to mount to that point. At the time of inserting CDROM into the system, the corresponding CDROM file system will automatically mounts to the directory - /dev/cdrom in the system. The unmount system call is used to detach a file system.

Using the mknod command, special files can be created.   

Mknod [options] name type[major minor]

Here, if argument is “p” a named pipe of FIFO file is created.

If the argument is “b”, a block file is created. Here, the major or minor device numbers needs to be specified. If the argument is “c or u”, a character file is created. Here, the major or minor device numbers needs to be specified.

Special files are created by the system call ‘mknod’. Upon using the following sequence of steps, a special file will be created.

-new inode is assigned by kernel  -sets the file type as a pipe, directory or special file  -Major and minor device numbers are the two entries created if the file type is a device file.  For example, for a disk, disk controller is the major device number and the disk is the minor device is the disk. Unix example: $ mknod <pipe name> p

A link is a pointer or reference to another file. A directory in UNIX has a list of file names and their corresponding inodes. A directory entry can have an Inode pointing to another file. This is a hard link. When a hard link is made, then the i-numbers of two different directory file entries point to the same inode. A symbolic link or a soft link is a special type of file containing links or references to another file or directory in the form of a path. The path may be relative or absolute. To create a symbolic link, following command is used:

Ln –s target link_name

Here, target is the path and link_name is the name of the link. Symbolic links can be created to create a file system based on different views of the user.

Link is a utility program in UNIX which establishes a hard link from one directory to another directory. A hard link is a reference to a directory or to file on storage media. A symbolic link is a type of file. It contains references to another file directory in the form of absolute or a relative path.

Unix system calls for I/O

- creat(name, permissions) – Used to create a file with the name and mode specified. Here, permission would be a number. 0666 means read write permissions. - open(name, mode) – Used to open a file name in the mode (read or write) specified.0 is for opening in read mode, 1 for writing and 2 for both. - close(fd) – Close a opened file. - unlink(fd) – Delete a file. - read(fd, buffer, n_to_read) – Read data from a file. - write(fd, buffer, n_to_write) - write data from to a file. - lseek(fd, offest, whence) - Move the read/write pointer to the specified location.

The following are the UNIX system calls for I/O: - Open: to open a file.  Syntax:

open (pathname, flag, and mode).

- Create: To create a file.  Syntax:

create (pathname, mode).

- Close: To close a file. Syntax:

close (filedes).

- Read: To read data from a file that is opened.  Syntax:

read (filedes, buffer, bytes)

- Write: To write data to a file that is opened. Syntax:

write (filedes, buffer, bytes)

- Lseek: To position the file pointer at given location in the file. Syntax:

lseek (filedes, offset, from).

- Dup: To make a duplicate copy of an existing file descriptor. Syntax:

dup (filedes).

- Fcntl: To make the changes to the properties of an open file. Syntax:

fcntl (filedes, cmd, arg).

- Expansion swap is a part of hard disk. - This is reserved for the purpose of storing chunks of a program that is executing which is swapped out of the memory in order to make space available for other programs. - When process requires more memory that it is currently allocated at the time of process execution, the kernel performs expansion swap. - Kernel reserves enough space in the swap device.

For creation of child process, fork() system call is invoked. At the time of processing the fork() call by parent, the child process is created. In case of shortage of memory, the child process will be sent to the read-to-run state in the swap device. It returns to the user state without performing the swapping the state of parent. Once the memory is available, the child process swapping is done into the main memory.

This contains the private data that is manipulated only by the Kernel. This is local to the Process, i.e. each process is allocated a u-area.

U-area is assosiated with executing process, process accesses all the process related information and set up environment that process can execute easily, without need to worry of process table entries

It decides which process should reside in the main memory, Manages the parts of the virtual address space of a process which is non-core resident, Monitors the available main memory and periodically write the processes into the swap device to provide more processes fit in the main memory simultaneously.

Historic Unix uses Swapping – entire process is transferred to the main memory from the swap device, whereas the Unix System V uses Demand Paging – only the part of the process is moved to the main memory. Historic Unix uses one Swap Device and Unix System V allow multiple Swap Devices.

In a Unix-style file system, the inode is a data structure used to represent a filesystem object, which can be one of various things including a file or a directory. Each inode stores the attributes and disk block location(s) of the filesystem object's data.

Devices in UNIX are represented by files. These are special files located in the )dev directory. Hence in UNIX, every piece of hardware is a file. This device file allows us to access the hardware. For instance, the following command; Less –f /dev/hda is not a file in the ‘real’ sense. When read, it is actually reading directly from the first physical hard disk of your machine

UNIX represents all devices as files. These files are located in the directory /dev. That is why the devices and other files are accessed in a similar way. Devices file which is specified as ‘block special file’ with some similar characters of a disk file. A device which is specified as a ‘character special file’ with some characteristics that is similar to a keyboard.

Preemptive multitasking is one of the most common types of computer multitasking techniques. It works on a time sharing feature, where each process may be allocated equal shares of computing resources. However, depending on a task's criticality and priority, additional time may be allocated.

For example, OS-specific background tasks may be considered more important than a user application’s tasks. Thus, they receive larger time slices than forefront tasks.

Preemptive multitasking is a type of multitasking that allows computer programs to share operating systems (OS) and underlying hardware resources. It divides the overall operating and computing time between processes, and the switching of resources between different processes occurs through predefined criteria.

Preemptive multitasking is also known as time-shared multitasking.

To prevent a program from taking control of computing resources, preemptive multitasking restricts the program to limited time slices.

Plumbing

Alternatively referred to as piping, plumbing describe a feature found in Linux, Unix, and other operating systems where the output of one program is sent as input to another program. This feature is useful for when a user needs data from one program and does not want to have to retype all the output.

• An example of a Linux and Unix command that takes advantage of plumbing is the tee command.

A network operating system (NOS) is a computer operating system system that is designed primarily to support workstation, personal computer, and, in some instances, older terminal that are connected on a local area network (LAN). Artisoft's LANtastic, Banyan VINES, Novell's NetWare, and Microsoft's LAN Manager are examples of network operating systems. In addition, some multi-purpose operating systems, such asWindows NT and Digital's OpenVMS come with capabilities that enable them to be described as a network operating system.

The salient features of network operating systems are:

• Basic operating system features support like protocol support, processor support, hardware detection and multiprocessing support for applications
• Security features like authentication, restrictions, authorizations and access control
• Features for file, Web service, printing and replication
• Directory and name services management
• User management features along with provisions for remote access and system management
• Internetworking features like routing and WAN ports
• Clustering capabilities

Common tasks associated with network operating systems include:

• User administration
• System maintenance activities like backup
• Tasks associated with file management
• Security monitoring on all resources in the network
• Setting priority to print jobs in the network

An interrupt is a signal from a device attached to a computer or from a program within the computer that causes the main program that operates the computer (the operating system ) to stop and figure out what to do next. Almost all personal (or larger) computers today areinterrupt-driven - that is, they start down the list of computer instruction s in one program (perhaps an application such as a word processor) and keep running the instructions until either (A) they can't go any further or (B) an interrupt signal is sensed. After the interrupt signal is sensed, the computer either resumes running the program it was running or begins running another program.

In general, there are hardware interrupts and software interrupts. A hardware interrupt occurs, for example, when an I/O operation is completed such as reading some data into the computer from a tape drive. A software interrupt occurs when an application program terminates or requests certain services from the operating system. In a personal computer, a hardware interrupt request ( IRQ ) has a value associated with it that associates it with a particular device.

An assembler is a program that takes basic computer instructions and converts them into a pattern of bits that the computer's processor can use to perform its basic operations. Some people call these instructions assembler language and others use the term assembly language.

An assembler primarily serves as the bridge between symbolically coded instructions written in assembly language and the computer processor, memory and other computational components. An assembler works by assembling and converting the source code of assembly language into object code or an object file that constitutes a stream of zeros and ones of machine code, which are directly executable by the processor.

Assemblers are classified based on the number of times it takes them to read the source code before translating it; there are both single-pass and multi-pass assemblers. Moreover, some high-end assemblers provide enhanced functionality by enabling the use of control statements, data abstraction services and providing support for object-oriented programming structures.

Spooling is an acronym for simultaneous peripheral operations on line. Spoolingrefers to putting data of various I/O jobs in a buffer. This buffer is a special area in memory or hard disk which is accessible to I/O devices.

• OS handles I/O device data spooling as devices have different data access rates.

• OS maintains the spooling buffer which provides a waiting station where data can rest while the slower device catches up.

• OS maintains parallel computation because of spooling process as a computer can perform I/O in parallel fashion. It becomes possible to have the computer read data from a tape, write data to disk and to write out to a tape printer while it is doing its computing task.

Advantages

• The spooling operation uses a disk as a very large buffer.

• Spooling is capable of overlapping I/O operation for one job with processor operations for another job.

Caching (pronounced “cashing”) is the process of storing data in a cache.

A cache is a temporary storage area. For example, the files you automatically request by looking at a Web page are stored on your hard disk in a cache subdirectory under thedirectory for your browser. When you return to a page you've recently looked at, the browser can get those files from the cache rather than the original server, saving you time and saving the network the burden of additional traffic.

The pros It's faster: It's well-known that in most cases the use of command-line is faster and makes easier working with large numbers of files Easily automate tasks through scripts: Scripts and functions can prove very handy for certain tasks which need to be performed on a regular basis Aliases: A strong point of the shell is the ability to create aliases, which usually replace a longer command (or small group of commands) with an easy to type one More powerful: In most cases CLI is more powerful. Just an example, when it comes to manipulating a big number of files CLI is the way to go, since it can perform custom operations using several commands which usually fit on a single line very fast Faster for getting help: It's faster to get help by copying and pasting a command (given that you know what it does) than through screenshots; bandwidth is one factor, another one is different desktop environments (e.g. use Synaptic/KPackage, go there, under that button, press that etc, instead of just apt-get install something) Less memory: Using CLI won't load additional GUI libraries (given they aren't already loaded) Less bandwidth: Although today bandwidth is not a major factor any more, using CLI for navigating on the Internet saves bandwidth and is faster Basic CLI knowledge can make wonders: CLI can be successfully used on a very old computer, and you can browse the web, listen to music, use IRC and IM, read mail etc without any problems. A minimum CLI knowledge will also help troubleshooting a computer for which X won't start etc GUI frontends can be incomplete: With CLI, you have complete power over the parameters to pass to a command-line tool. Sometimes GUI frontends lack those

The cons Making mistakes: Running commands and scripts in a wrong manner (especially if one doesn't know what the specific command does) can lead to unwanted removal of files, a broken system and so on Lack of GUI: Although you can browse the web, see images and even videos (using ASCII), it's obviously using CLI for that isn't the optimum way. Of course, this also depends on one's needs, but browsing the web for example with a text-based browser is usually slower and lacks images, videos etc. GUI is definitely more intuitive: And also, more easy to remember things. Since the brain memorizes images too, GUI will be easier to use for the average user GUI looks good: I guess it's always nicer to look at KDE4 effects or Compiz than at a screen full of text note: over 95% of the Linux users have a GUI, and although one can use a computer only with CLI, it makes no sense to use only CLI if you also need to do tasks which require a GUI.

A thread (also called a task) is a sequential path of execution. The discrete statements of a thread are processed sequentially according to the semantics of C, C++, or Pascal.

The term multitasking means that several sequential tasks are processed in parallel. However, on single processor systems, several tasks cannot run at the same time; therefore, task switches must be performed. This is the job of a multitasking system like RTKernel-32.

In many cases, tasks cannot run completely independently of each other, but are expected to cooperate. For example, it may be required that a certain task can only continue to run after another task has completed a certain operation. In such a case, the tasks involved must be synchronized, i.e., the parallelism of tasks is restricted again. Synchronization can be accomplished using inter-task communication.

For a good understanding of parallel programming, it is important to be aware of the different requirements of multitasking systems. 

Time Sharing

Time sharing utilizes multitasking for the purpose of sharing a high performance computer among several users (or batch jobs) at the same time. In general, tasks run largely independently of each other in time sharing systems. Therefore, inter-task communication is only offered in a simple fashion.

One of the most popular time sharing systems is Unix. It was developed when the processing power of the available computer was smaller than that needed for the job. Consequently, the multitasking system had to share the scarce resource "processing power" as "fairly" as possible among competing tasks. However, it should be noted that system throughput is usually degraded by multitasking in such systems, because the scheduling overhead is significant. Under Unix, for example, it is possible that two compute-bound programs each runs a minute when it is the only program running; however, running in parallel, they would need 2.5 minutes. Parallel processing may be more fair (User 1 and User 2 have to wait equally long for their job to finish), but is usually less efficient.

Real-Time Systems

Real-time systems satisfy a completely different set of requirements. A real-time system must never be overloaded. As soon as no more processing power is available, real-time response cannot be sustained. For example, a situation with real-time requirements might be: a meter generates data every second. The data must be collected, processed, and stored by the computer. If processing a data record requires more than a second on the target computer, the system is overloaded and real-time response cannot be sustained.

Real-time systems are not concerned about "fairness". Tasks have priorities which must be obeyed strictly. A task with a high priority can take away CPU time from another task with a lower priority at any time without "being fair" to the other task. Since overloading is ruled out, tasks having low priorities will sooner or later also receive CPU time.

Real-time systems are furthermore characterized by the requirement that they have to react to events within a predetermined - usually short - time span. External events are processed using interrupts whenever possible. Thus, the most stringent real-time requirements apply to interrupt handlers. Therefore, real-time systems must have a low interrupt latency (the time between the hardware interrupt signal and execution of the first statement of the interrupt handler).

For the task response time, the cases of cooperative and preemptive scheduling must be distinguished. In preemptive scheduling, the task response time to interrupts is mainly the interrupt latency and the task switch time. In cooperative scheduling, the maximum time span between two kernel calls is added.

Cooperative and Preemptive Multitasking

Preemptive multitasking means that task switches can be initiated directly out of interrupt handlers. With cooperative (non-preemptive) multitasking, a task switch is only performed when a task calls the kernel, i.e., it behaves "cooperatively" and voluntarily gives the kernel a chance to perform a task switch.

An I/O port typically consists of four registers, called the status ,control,data-in, and data-out registers.

S.N.Register & Description

1.Status Register The status register contains bits that can be read by the host. These bits indicate states such as whether the current command has completed, whether a byte is available to be read from the data-in register, and whether there has been a device error.

2.Control register The control register can be written by the host to start a command or to change the mode of a device. For instance, a certain bit in the control register of a serial port chooses between full-duplex and half-duplex communication, another enables parity checking, a third bit sets the word length to 7 or 8 bits, and other bits select one of the speeds supported by the serial port.

3. Data-in register The data-in register is read by the host to get input.

4.Data-out register The data out register is written by the host to send output.

Different types of CPU registers in a typical operating system design

- Accumulators

- Index Registers

- Stack Pointer

- General Purpose Registers

VFS, or Virtual File System, separates file system generic operations from their implementation by defining a clean VFS interface. It is also based on a file-representation structure known as vnode, which contains a numerical designator needed to support network file systems.

A device driver is a program that controls a particular type of device that is attached to your computer. There are device drivers for printers, displays, CD-ROM readers, diskette drives, and so on. When you buy an operating system, many device drivers are built into the product.

The root file system is the file system contained on the same disk partition on which the root directory is located; it is the filesystem on top of which all other file systems are mounted as the system boots up.

In computer storage, direct access is the ability to obtain data from a storage device by going directly to where it is physically located on the device rather than by having to sequentially look for the data at one physical location after another. A direct access storage device (DASD) has the electrical or electromechanical means to be immediately positioned for reading and writing at any addressable location on the device.An alternative to direct access is sequential access, in which a data location is found by starting at one place and seeking through every successive location until the data is found. Historically, tape storage is associated with sequential access, and disk storage is associated with direct access.

Home Dictionary Tags Storage Fragmentation Definition - What does Fragmentation mean? Fragmentation, in the context of a hard disk, is a condition in which the contents of a single file are stored in different locations on the disk rather than in a contiguous space. This results in inefficient use of storage space as well as occasional performance degradation. Users frequently create, modify, delete and save files. Back-end operating systems (OS) continuously store these files on hard drives, which inevitably creates scattered files. When fragmentation occurs, the OS needs to consolidate stored files to enhance processing efficiency.

Logical Vs physical address space (1) An address generated by the CPU is commonly referred to as a logical a logical address. The set of all logical addresses generated by a program is known as logical address space. Whereas, an address seen by the memory unit- that is, the one loaded into the memory-address register of the memory- is commonly referred to as physical address. The set of all physical addresses corresponding to the logical addresses is known as physical address space. (2) The compile-time and load-time address-binding methods generate identical logical and physical addresses. However, in the execution-time address-binding scheme, the logical and physical-address spaces differ. (3) The user program never sees the physical addresses. The program creates a pointer to a logical address, say 346, stores it in memory, manipulate it, compares it to other logical addresses- all as the number 346. Only when a logical address is used as memory address, it is relocated relative to the base/relocation register. The memory-mapping hardware device called the memory- management unit(MMU) converts logical addresses into physical addresses. (4) Logical addresses range from 0 to max. User program that generates logical address thinks that the process runs in locations 0 to max. Logical addresses must be mapped to physical addresses before they are used. Physical addresses range from (R+0) to (R + max) for a base/relocation register value R. Mapping from logical to physical addresses using memory management unit (MMU) and relocation/base register The value in relocation/base register is added to every logical address generated by a user process, at the time it is sent to memory, to generate corresponding physical address. In the above figure, base/ relocation value is 14000, then an attempt by the user to access the location 346 is mapped to 14346.

The benefits of multithreaded programming can be broken down into four major categories:

Responsiveness

Multithreading an interactive application may allow a program to continue running even if part of it is blocked or is performing a lengthy operation, thereby increasing responsiveness to the user.

For instance, a multithreaded web browser could still allow user interaction in one thread while an image was being loaded in another thread.

Resource sharing

By default, threads share the memory and the resources of the process to which they belong. The benefit of sharing code and data is that it allows an application to have several different threads of activity within the same address space.

Economy

Allocating memory and resources for process creation is costly. Because threads share resources of the process to which they belong, it is more economical to create and context-switch threads. Empirically gauging the difference in overhead can be difficult, but in general it is much more time consuming to create and manage processes than threads.

In Solaris, for example, creating a process is about thirty times slower than is creating a thread, and context switching is about five times slower.

Utilization of multiprocessor architectures

The benefits of multithreading can be greatly increased in a multiprocessor architecture, where threads may be running in parallel on different processors. A single threaded process can only run on one CPU, no matter how many are available.

Traditional J2EE application servers work well for a large class of applications. This class can broadly be categorized as applications that run in a stateless cluster in front of a database. We can call this a symmetric cluster:

– All the cluster members can perform any task at any time.

– The application is stateless.

– The application is modal which means it only performs work synchronously in response to a client request which can be received using HTTP/IIOP or JMS.

There are other applications that do not work well in such an environment, for example, an electronic trading system in a bank. Such applications typically use tricks that can greatly improve performance such as partitioning, multi-threading and write through caching. These are applications that can exploit asymmetric clustering. An asymmetric cluster is practically the opposite of a symmetric cluster:

– applications can declare named partitions at any point while it’s running

– partitions are highly available uniquely named singletons and run on a single cluster member at a time

– incoming work for a partition is routed to the cluster member hosting the partition

– The application is amodal. Partitions have a lifecycle of their own and can start background threads/alarms as well as respond to incoming events whether they are IIOP/HTTP or JMS/foreign messages.

WebSphere XD offers a new set of programming API’s called the “Partitioning Facility”. These APIs allow applications that require an asymmetric cluster to be deployed on a J2EE server for the first time to my knowledge.

The main objective of multiprogramming is to have process running at all times. With this design, CPU utilization is said to be maximized.

minimise unused CPU time reduce incidence of peripheral-bound operations minimise total elapsed time prevent single programs from dominating the CPU

Virtual memory (VM) is a feature developed for the kernel of an operating system (OS) that simulates additional main memory such as RAM (random access memory) or disc storage. This technique involves the manipulation and management of memory by allowing the loading and execution of larger programs or multiple programs simultaneously. It also allows each program to operate as if it had infinite memory, and is often considered more cost effective than purchasing additional RAM. Virtual memory permits software to use additional memory by utilizing the hard disc drive (HDD) as temporary storage. Most central processing units (CPUs) provide memory management units (MMUs) that support virtual memory. The MMU supports the “page tables” that are used to transform the “real” and “virtual” addresses located in memory and on the HDD. An OS that uses virtual memory frees up space by transferring data from the HDD which is not immediately required. When the data is needed, it is copied back to the HDD. When all RAM is being used, VM swaps data to the HDD and then back again. Thus, VM allows a larger total system memory; however, complicated code writing is required.

Real-Time systems span several domains of computer science. They are defense and space systems, networked multimedia systems, embedded automative electronics etc. In a real-time system the correctness of the system behavior depends not only the logical results of the computations, but also on the physical instant at which these results are produced. A real-time system changes its state as a function of physical time, e.g., a chemical reaction continues to change its state even after its controlling computer system has stopped. Based on this a real-time system can be decomposed into a set of subsystems i.e., the controlled object, the real-time computer system and the human operator. A real-time computer system must react to stimuli from the controlled object (or the operator) within time intervals dictated by its environment. The instant at which a result is produced is called a deadline. If the result has utility even after the deadline has passed, the deadline is classified as soft, otherwise it is firm. If a catastrophe could result if a firm deadline is missed, the deadline is hard. Commands and Control systems, Air traffic control systems are examples for hard real-time systems. On-line transaction systems, airline reservation systems are soft real-time systems.

The operating system serves many purposes. Talking at a high level operating system can be cosidered as a translator between user and computer(CPU).CPU or processor can understand only 0s and 1s, but the programs that we use today are written in somehigh level language like C or Java or something else. Now these programs ultimately had to be changed to 0s and 1s inorder to execute. This is the responsibility of Operating System. Then comes multitasking, we can execute multiple programs simultaneously in a single CPU, so this single execution core is shared among programs. This CPU management is also onus of Operating System.Not only CPU managent but many other resources are managed by Operatimg System like memory. Speaking at low level you cannot imagine a computer without Operating System. To facilitate access to the workings of the machine, which at its core only deals in zeros and ones. Without an operating system, you would have to manually type in instructions to the computer using machine code or a low-level language, and call functions.  It would take several hours to be able to perform simple tasks such as typing word documents!  Operating systems pre-load all the commands, information, and configurations the computer needs to perform tasks automatically, easily, and using a simple interface, such as mouse point-and-click or voice command, as well as streamlining general use and allowing simplified keyboard commands like control-alt-delete

DDKs are windows Device Driver kits which are popularly  known to be the developement environments for developing  windows device drivers for virtually any type of device  available today in the market. Microsoft has released it's first DDK for developing device  drivers for it's first ever popular desktop GUI OS windows  3.0 from that time onwards they have regularly released a  range of DDKs for many diffrent windows OS platforms like  win 3.11,win95,win98,millenium edition,windows  NT,win2k,win2003,winxp,win vista etc.

No Windows NT is not so, because its not implemented in object oriented language and the data structures reside within one executive component and are not represented as objects and it does not support object oriented capabilities

Short for Symmetric Multi-Processing, SMP is processing that is performed by multiple processors sharing the same operating system and computer memory. Most systems utilizing SMP do not exceed 16 processors.

With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices

Load time dynamic linking is usually accomplished by statically linking your application to a .lib or .a file that contains the code for automatically establishing runtime links to symbols to be found in .dll or .so files at program startup. This is usually for fixed functionality (i.e. the C runtime library, etc.) and allows your program to reap the benefits of bug fixes in the libraries while keeping executable size small (by factoring common code into a single library).

Runtime linking is used for more dynamic functionality such as plugin loading. As Aiden said, you use LoadLibrary() or the equivalent to actively attach modules to your program at runtime, perhaps by interrogating a directory containing plugin DLLs, loading each one in turn and talking to it with a homegrown plugin API. By doing so, your program can load modules that did not even exist when your app was compiled/linked, and can thus grow organically after deployment.

Fundamentally both methods end up invoking the LoadLibrary() API, but using a fixed set of symbols and libraries in the former case and a more dynamic set in the latter.

In computing timestamping refers to the use of an electronic timestamp to provide a temporal order among a set of events. Timestampingtechniques are used in a variety of computing fields, from network management and computer security to concurrency control.

A trap is a device which is used to detect , capture and harm to an intruder.

A trap door is a secret entry point into a program that allows someone to gain access without normal methods of access authentication.

Busy waiting is where a process checks repeatedly for a condition- it is "waiting" for the condition, but it is "busy" checking for it. This will make the process eat CPU (usually)

Turnaround time is the interval between the submission of a  job and its completion.  Response time is the interval between submission of a  request, and the first response to that request.

Operating systems may feature up to 3 distinct types of schedulers: a long-term scheduler (also known as an admission scheduler or high-level scheduler), a mid-term or medium-term scheduler and a short-term scheduler . The names suggest the relative frequency with which these functions are performed.

Long-term scheduler

• The long-term, or admission, scheduler decides which jobs or processes are to be admitted to the ready queue; that is, when an attempt is made to execute a program, its admission to the set of currently executing processes is either authorized or delayed by the long-term scheduler. Thus, this scheduler dictates what processes are to run on a system, and the degree of concurrency to be supported at any one time - ie: whether a high or low amount of processes are to be executed concurrently, and how the split between IO intensive and CPU intensive processes is to be handled. In modern OS's, this is used to make sure that real time processes get enough CPU time to finish their tasks. Without proper real time scheduling, modern GUI interfaces would seem sluggish.

• Long-term scheduling is also important in large-scale systems such as batch processing systems, computer clusters, supercomputers and render farms. In these cases, special purpose job scheduler software is typically used to assist these functions, in addition to any underlying admission scheduling support in the operating system.

Mid-term scheduler

• The mid-term scheduler temporarily removes processes from main memory and places them on secondary memory (such as a disk drive) or vice versa. This is commonly referred to as "swapping out" or "swapping in" (also incorrectly as "paging out" or "paging in"). The mid-term scheduler may decide to swap out a process which has not been active for some time, or a process which has a low priority, or a process which is page faulting frequently, or a process which is taking up a large amount of memory in order to free up main memory for other processes, swapping the process back in later when more memory is available, or when the process has been unblocked and is no longer waiting for a resource.

• In many systems today (those that support mapping virtual address space to secondary storage other than the swap file), the mid-term scheduler may actually perform the role of the long-term scheduler, by treating binaries as "swapped out processes" upon their execution. In this way, when a segment of the binary is required it can be swapped in on demand, or "lazy loaded".

Short-term scheduler

• The short-term scheduler (also known as the CPU scheduler) decides which of the ready, in-memory processes are to be executed (allocated a CPU) next following a clock interrupt, an IO interrupt, an operating system call or another form of signal. Thus the short-term scheduler makes scheduling decisions much more frequently than the long-term or mid-term schedulers - a scheduling decision will at a minimum have to be made after every time slice, and these are very short. 

• This scheduler can be preemptive, implying that it is capable of forcibly removing processes from a CPU when it decides to allocate that CPU to another process, or non-preemptive (also known as "voluntary" or "co-operative"), in which case the scheduler is unable to "force" processes off the CPU.

User data: Modifiable part of user space. May include  program data, user stack area, and programs that may be  modified.  User program: The instructions to be executed. System Stack: Each process has one or more LIFO stacks  associated with it. Used to store parameters and calling  addresses for procedure and system calls. Process control Block (PCB): Info needed by the OS to  control processes

If a process in a monitor signal and no task is waiting on the condition variable, the signal is lost. So this allows easier program design. Whereas in semaphores, every operation affects the value of the semaphore, so the wait and signal operations should be perfectly balanced in the program

Seek time is the time required to move the disk arm to the required track. Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if any) and latency is the access time. Time taken to actually transfer a span of data is transfer time. 

C2 level security provides for:

• Discretionary Access Control
• Identification and Authentication
• Auditing
• Resource reuse

We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation. The latter technique is called cycle stealing. Note that cycle stealing can be done only at specific break points in an instruction cycle.

Resident set is that portion of the process image that is actually in real-memory at a particular instant. Working set is that subset of resident set that is actually needed for execution. (Relate this to the variable-window size method for swapping techniques).

A translation lookaside buffer (TLB) is a memory cache that stores recent translations ofvirtual memory to physical addresses for faster retrieval.

When a virtual memory address is referenced by a program, the search starts in the CPU. First, instruction caches are checked. If the required memory is not in these very fast caches, the system has to look up the memory’s physical address. At this point, TLB is checked for a quick reference to the location in physical memory.

When an address is searched in the TLB and not found, the physical memory must be searched with a memory page crawl operation. As virtual memory addresses are translated, values referenced are added to TLB. When a value can be retrieved from TLB, speed is enhanced because the memory address is stored in the TLB on processor. Most processors include TLBs to increase the speed of virtual memory operations through the inherent latency-reducing proximity as well as the high-running frequencies of current CPU’s.

TLBs also add the support required for multi-user computers to keep memory separate, by having a user and a supervisor mode as well as using permissions on read and write bits to enable sharing.

TLBs can suffer performance issues from multitasking and code errors. This performance degradation is called a cache thrash. Cache thrash is caused by an ongoing computer activity that fails to progress due to excessive use of resources or conflicts in the caching system.

Mutual Exclusion: Only one process may use a critical resource at a time. Hold & Wait: A process may be allocated some resources while waiting for others. No Pre-emption: No resource can be forcible removed from a process holding it. Circular Wait: A closed chain of processes exist such that each process holds at least one resource needed by another process in the chain

In a virtual storage system (an operating system that manages its logical storage or memory in units called pages), thrashing is a condition in which excessive paging operations are taking place. A system that is thrashing can be perceived as either a very slow system or one that has come to a halt.

A binary semaphore is one, which takes only 0 and 1 as  values. They are used to implement mutual exclusion and  synchronize concurrent processes 

Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns. In computer storage, Bélády's anomaly is the name given to the phenomenon where increasing the number of page frames results in an increase in the number of page faults for a given memory access pattern. This phenomenon is commonly experienced when using the First in First Out (FIFO) page replacement algorithm.

It is a useful, memory-saving technique for multiprogrammed time sharing systems. A Reentrant Procedure is one in which multiple users can share a single copy of a program during the same period. Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each user process must be stored separately. Thus, the permanent part is the code, and the temporary part is the pointer back to the calling program and local variables used by that program. Each execution instance is called activation. It executes the code in the permanent part, but has its own copy of local variables/parameters. The temporary part associated with each activation is the activation record. Generally, the activation record is kept on the stack.

One is that it depends on how often a deadlock is likely to occur under the implementation of this algorithm. The other has to do with how many processes will be affected by deadlock when this algorithm is applied.

Round robin  is the  scheduling algorithm used by the CPU during execution of the process . Round robin is designed specifically for time sharing systems . It is similar to first come first serve scheduling algorithm but the preemption  is the added functionality to switch between the processes . A small unit of time also known as time slice or quantum is set/defined . The ready queue works like circular queue .All processes in this algorithm are kept in the circular queue also known as ready queue .  Each New process is added to the tail of the ready/circular queue . By using this algorithm , CPU makes sure, time slices ( any natural number ) are assigned  to each process in equal portions and in circular order , dealing with all process without any priority . It is also known as cyclic executive . The main advantage of round robin algorithm over first come first serve algorithm is that it is  starvation free  . Every process will be executed by CPU for fixed interval of time (which is set as time slice ) . So in this way no process left waiting for its turn to be executed by the CPU . Round robin algorithm is simple and easy to implement . The  name round robin comes from the principle known as round robin in which every person takes equal share of something in turn .

The best paging size varies from system to system, so there is no single best when it comes to page size. There are different factors to consider in order to come up with a suitable page size, such as page table, paging time, and its effect on the overall efficiency of the operating system.

Principle of Locality

When a program executes on a computer, most of the memory references are not made uniformly to a small number of locations. Here the Locality of the reference does matter. Locality of Reference, also known as the Principle of Locality, the phenomenon of the same value or related storage locations being frequently accessed. Locality occurs in time(temporal locality) and in space (spatial locality).

• Temporal Locality refers to the reuse of specific data and/or resources within relatively small time durations.
• Spatial Locality refers to the use of data elements within relatively close storage locations. Sequential locality, a special case of spatial locality, occurs when data elements are arranged and accessed linearly, eg, traversing the elements in a one-dimensional array.

To be very simple when exhibiting spatial locality, a program accesses consecutive memory locations and during temporal locality of reference a program repeatedly accesses the same memory location during a short time period. Both forms of locality occur in the following Pascal code segment:

for i := 0 to 10 do A [i] := 0;

In the above Pascal code, the variable 'i' is referenced several times in for loop where 'i' is compared against 10 to see if the loop is complete and also incremented by one at the end of the loop. This shows temporal locality of reference in action since the CPU accesses 'i' at different points in a short time period. This program also exhibits spatial locality of reference. The loop itself zeros out the elements of array A by writing a zero to the first location in A, then to the second location in A, and so on. Assume Pascal stores elements of A into consecutive memory locations then on each loop iteration it accesses adjacent memory locations.

The functionality of a swapper is on the scheduling priority which is highest. The swapper searches for sleeping process. It searches for the processes that are ready to run for swapping, if the sleeping process not found.  The requirement for the swapper is to work for the process that is ready to run and must be the resident for at least 2 seconds before swapping out. The process must be resided in the swap device for at least 2 seconds, for any swapping. The swapper will go into the wait state, if the requirement is not satisfied, for that event. It will be awaken once in a second by the kernel of the OS.

Every statement has a truth value, that is, every statement is true or false. The truth value of a truth-functional compound proposition is determined by the truth values of its components and the definitions of the logical operators involved. Any truth-functional compound proposition that can be determined in this manner is called a “truth function.”

Fault handlers are also an interrupt handler with an exception that the interrupt handlers cannot sleep. Fault handlers sleep in the context of the process that caused the memory fault. The fault refers to the running process and no arbitrary processes are put to sleep.

Map Rolling

A pair, quad or an octet can be formed by combining the adjacent ones in rectangular form. A combination can also be obtained by rolling the map (just like a world map is rolled to combine the left-most and right- most edges) along its length or width. This is called map rolling.

Redundant groups

A groups of 1s or 0s whose all members are overlapped by other groups is called redundant group. We don’t consider this group while writing the simplified equations from the K-map.

Idempotent Law – An input that is AND´ed or OR´ed with itself is equal to that input.

• A + A = A    A variable OR’ed with itself is always equal to the variable.
• A . A = A     A variable AND’ed with itself is always equal to the variable.

The principal threat of Internet censorship today is the Communications Decency Act, a law passed by Congress and signed by the President in January, 1996 which would apply quite radical regulations to speech on the Internet.

WAIS (Wide Area Information Servers) is an Internet system in which specialized subject databases are created at multiple server locations, kept track of by a directory of servers at one location, and made accessible for searching by users with WAIS client programs. The user of WAIS is provided with or obtains a list of distributed database s. The user enters a search argument for a selected database and the client then accesses all the servers on which the database is distributed. The results provide a description of each text that meets the search requirements. The user can then retrieve the full text.

WAIS (pronounced "ways") uses its own Internet protocol , an extension of the Z39.50 standard (Information Retrieval Service Definition and Protocol Specification for Library Applications) of the National Information Standards Organization. Web users can use WAIS by either downloading a WAIS client and a "gateway" to the Web browser or by using Telnetto connect to a public WAIS client.

Take the 2 addresses, write them in binary form, then AND them. The answer is 130.40.32.0 

The subnet address in the IP address with the network address and without host bits. To find it we do an AND operation between the IP address and the subnet mask.  Converting 130.40.32.16 to binary:  10000010.00101000.00100000.00010000  Converting the subnet mask 255.255.248.0 to binary:  11111111.11111111.11111000.00000000  AND-ing the two binaries we get:  10000010.00101000.00100000.00000000  Back to decimal we get: 130.40.32.0

Experts often contrast a two-tier architecture to a three-tier architecture, where a third application or business layer is added that acts as an intermediary between the client or presentation layer and the data layer. This can increase the performance of the system and help with scalability. It can also eliminate many kinds of problems with confusion, which can be caused by multi-user access in two-tier architectures. However, the advanced complexity of three-tier architecture may mean more cost and effort.

An additional note on two-tier architecture is that the word "tier" commonly refers to splitting the two software layers onto two different physical pieces of hardware. Multi-layer programs can be built on one tier, but because of operational preferences, many two-tier architectures use a computer for the first tier and a server for the second tier.

A two-tier architecture is a software architecture in which a presentation layer or interface runs on a client, and a data layer or data structure gets stored on a server. Separating these two components into different locations represents a two-tier architecture, as opposed to a single-tier architecture. Other kinds of multi-tier architectures add additional layers in distributed software design.

ASMP

(ASymmetric MultiProcessing) A multiprocessing design in which each CPU is assigned a particular program or part of a program that it executes for the duration of the session. Contrast with SMP, in which all the CPUs function as a single resource pool and take on whatever tasks need to be processed next. 

Kerberos uses encryption technology and a trusted third party, an arbitrator, to perform secure authentication on an open network. Specifically, Kerberos uses cryptographic tickets in order to avoid transmitting plain text passwords over the wire. Kerberos was based upon the Needham-Schroeder protocol.

A twisted pair cable is a type of cable made by putting two separate insulated wires together in a twisted pattern and running them parallel to each other. This type of cable is widely used in different kinds of data and voice infrastructures twisted pair cabling is often used to help avoid certain kinds of signal interference. Two different types of twisted pair cable, unshielded twisted pair (UTP) and shielded twisted pair (STP) are used in different kinds of installations. UTP is common in Ethernet installations, while STP is used in various kinds of networks to prevent crosstalk and electromagnetic interference. STP cable can also help to provide grounding.

In general, twisted-pair cabling may be preferred over a common alternative, coaxial cable, for different reasons. Coaxial cable involves a single, thicker wire. Many of those who use this type of cable claim that twisted pair has a more accommodating bend radius, is easier to terminate, and provides more versatility in selecting network topologies. Different kinds of twisted-pair cable are rated by industry standards including ISO/EIC and EIA/TIA.

Most typical functional units of the Client/Server applications

User interface Business Logic and Shared data.

Telecom sector comes in layer3 that is network layer.

A host is a computer that is connected to a network. The term usually refers to a computer that is connected to a TCP/IP network, including the Internet. Each host on such a network has a unique IP address.

In information technology, a protocol is the special set of rules that end points in a telecommunication connection use when they communicate.Protocols specify interactions between the communicating entities.

Internet work have clear advantages over conventional methods, First, the use of the internet allows for rapid researching of sources and information access. Internet work creates and fosters real-time collaboration on projects and ideas often negating the need for in-person conferencing. Internet work can replace local data storage by placing information into virtual clouds as safer backups onto servers. Finally the 24-7 global nature of the internet permits constant operation at all times. This further increases productivity by ensuring virtually uninterrupted access to work and data.

In case we need less connection of wires, very fast communicatiin speed; a ring topology becomes the best choice for a network. This is because optical fiber offers the possibility of very high speed transmission in one direction. 

Internetworking is the process or technique of connecting different networks by using intermediary devices such as routers or gateway devices. Internetworking ensures data communication among networks owned and operated by different entities using a common data communication and the Internet Routing Protocol.

Cost of installation is high.

Expensive to use.

If the hub is affected then the whole network is stopped because all the nodes depend on the hub.

Performance is based on the hub that is it depends on its capacity

BUS Topology

Bus topology is a network type in where every computer and network device is connected to single cable.

Features of Bus Topology

It transmits data only in one direction. Every device is connected to a single cable

Advantages of Bus Topology

It is cost effective. Cable required is least compared to other network topology. Used in small networks. It is easy to understand. Easy to expand joining two cables together.

Disadvantages of Bus Topology

Cables fails then whole network fails. If network traffic is heavy or nodes are more the performance of the network decreases. Cable has a limited length. It is slower than the ring topology.

TREE Topology

It has a root node and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. It should at least have three levels to the hierarchy.

Features of Tree Topology

Ideal if workstations are located in groups. Used in Wide Area Network.

Advantages of Tree Topology

Extension of bus and star topologies. Expansion of nodes is possible and easy. Easily managed and maintained. Error detection is easily done.

Disadvantages of Tree Topology

Heavily cabled. Costly. If more nodes are added maintenance is difficult. Central hub fails, network fails.

• Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.
• Length of cable needed. The linear bus network uses shorter lengths of cable.
• Future growth. With a star topology, expanding a network is easily done by adding another concentrator.
• Cable type. The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.

Network topology refers to the physical or logical layout of a network. It defines the way different nodes are placed and interconnected with each other. Alternately, network topology may describe how the data is transferred between these nodes.

There are two types of network topologies: physical and logical. Physical topology emphasizes the physical layout of the connected devices and nodes, while the logical topology focuses on the pattern of data transfer between network nodes.

Some popular topologies.

The physical and logical network topologies of a network do not necessarily have to be identical. However, both physical and network topologies can be categorized into five basic models:

• Bus Topology: All the devices/nodes are connected sequentially to the same backbone or transmission line. This is a simple, low-cost topology, but its single point of failure presents a risk.
• Star Topology: All the nodes in the network are connected to a central device like a hub or switch via cables. Failure of individual nodes or cables does not necessarily create downtime in the network but the failure of a central device can. This topology is the most preferred and popular model.
• Ring Topology: All network devices are connected sequentially to a backbone as in bus topology except that the backbone ends at the starting node, forming a ring. Ring topology shares many of bus topology's disadvantages so its use is limited to networks that demand high throughput.
• Tree Topology: A root node is connected to two or more sub-level nodes, which themselves are connected hierarchically to sub-level nodes. Physically, the tree topology is similar to bus and star topologies; the network backbone may have a bus topology, while the low-level nodes connect using star topology.
• Mesh Topology: The topology in each node is directly connected to some or all the other nodes present in the network. This redundancy makes the network highly fault tolerant but the escalated costs may limit this topology to highly critical networks.

LAN, which stands for local area network, and WAN, which stands for wide area network, are two types of networks that allow for interconnectivity between computers. As the naming conventions suggest, LANs are for smaller, more localized networking — in a home, business, school, etc. — while WANs cover larger areas, such as cities, and even allow computers in different nations to connect. LANs are typically faster and more secure than WANs, but WANs enable more widespread connectivity. And while LANs tend to be owned, controlled and managed in-house by the organization where they are deployed, WANs typically require two or more of their constituent LANs to be connected over the public Internet or via a private connection established by a third-party telecommunications provider.

LAN

1. LAN (Local Area Network) is a computer network covering a small geographic area, like a home, office, schools, or group of buildings. 2. LAN has high speed (upto 1000mbps) 3. The best example for a LAN is the network in an organization. 4. The LAN is build using the layer 2 devices like switches, bridges and layer1 devices like hubs. 5. LAN is owned, controlled, and managed by a single person or organization 6. LAN is easier to maintain at relatively low costs. 7. LAN experiences fewer data transmission errors

WAN

1. WAN (Wide Area Network) is a computer network that covers a broad area. 2. WAN has less speed (upto 150mbps) 3. The best example for a WAN is the Internet 4. The WAN is build using the layers 3 devices Routers and Multi-layer Switches. 5. WAN's are not owned by any one organization but rather exist under distributed ownership. 6. Maintaining WAN is difficult because of its wider geographical coverage and higher maintenance costs. 7. WAN experiences more data transmission errors.

In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel.

In telecommunications and computer networking, a communication channel or channel, refers either to a physical transmission mediumsuch as a wire, or to a logical connection over a multiplexed medium such as a radio channel. A channel is used to convey an informationsignal, for example a digital bit stream, from one or several senders (or transmitters) to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.

A network interface unit (NIU) (sometimes called a network interface device) is a device that serves as a common interface for various other devices within a local area network (LAN), or as an interface to allow networked computers to connect to an outside network. The NIU enables communication between devices that use different protocols by supplying a common transmission protocol, which may be used instead of the devices' own protocols, or may be used to convert the specific device protocol to the common one. To enable an interface between a LAN and another network, the NIU converts protocols and associated code and acts as a buffer between the connected hardware. A network interface card (NIC) is a type of NIU. 

A Server is a computer or device on a network that manages network resources. For example, a file server is a computer and storage device dedicated to storing files Any user on the network can store files on the server. A print server is a computer that manages one or more printers and a network server is a computer that manages network traffic. Servers are often dedicated, meaning that they perform no other tasks besides their server tasks. On multiprocessing operating systems however, a single computer can execute several programs at once. A server in this case could refer to the program that is managing resources rather than the entire computer. What is Server Platform? A term often used synonymously with operating system. A platform is the underlying hardware or software for a system and is thus the engine that drives the server. Server types: Application Servers Sometimes referred to as a type of middleware, application servers occupy a large chunk of computing territory between database servers and the end user, and they often connect the two. Middleware is a software that connects two otherwise separate applications For example, there are a number of middleware products that link a database system to a Web server This allows users to request data from the database using forms displayed on a Web browser and it enables the Web server to return dynamic Web pages based on the user's requests and profile. The term middleware is used to describe separate products that serve as the glue between two applications. It is, therefore, distinct from import and export features that may be built into one of the applications. Middleware is sometimes called plumbing because it connects two sides of an application and passes data between them. Common middleware categories include:

* TP monitors * DCE environments * RPC systems * Object Request Brokers (ORBs) * Database access systems * Message Passing

Audio/Video Servers Audio/Video servers bring multimedia capabilities to Web sites by enabling them to broadcast streaming multimedia content. Streaming is a technique for transferring data such that it can be processed as a steady and continuous stream. Streaming technologies are becoming increasingly important with the growth of the Internet because most users do not have fast enough access to download large multimedia files quickly. With streaming, the client browser or plug-in can starts displaying the data before the entire file has been transmitted. For streaming to work, the client side receiving the data must be able to collect the data and send it as a steady stream to the application that is processing the data and converting it to sound or pictures. This means that if the streaming client receives the data more quickly than required, it needs to save the excess data in a buffer If the data doesn't come quickly enough, however, the presentation of the data will not be smooth. There are a number of competing streaming technologies emerging. For audio data on the Internet, the de facto standard is Progressive Network's RealAudio. Chat Servers Chat servers enable a large number of users to exchange information in an environment similar to Internet newsgroups that offer real-time discussion capabilities. Real time means occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systems are systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react. Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across the screen at the same speed that they would actually move. Fax Servers A fax server is an ideal solution for organizations looking to reduce incoming and outgoing telephone resources but that need to fax actual documents. FTP Servers One of the oldest of the Internet services, File Transfer Protocol makes it possible to move one or more files securely between computers while providing file security and organization as well as transfer control. Groupware Servers A GroupWare server is software designed to enable users to collaborate, regardless of location, via the Internet or a corporate Intranet and to work together in a virtual atmosphere. IRC Servers An option for those seeking real-time capabilities, Internet Relay Chat consists of various separate networks (or "nets") of servers that allow users to connect to each other via an IRC network. List Servers List servers offer a way to better manage mailing lists, whether they are interactive discussions open to the public or one-way lists that deliver announcements, newsletters, or advertising. Mail Servers Almost as ubiquitous and crucial as Web servers, mail servers move and store mail over corporate networks via LANs and WANs and across the Internet. News Servers News servers act as a distribution and delivery source for the thousands of public news groups currently accessible over the USENET news network. USENET is a worldwide bulletin board system that can be accessed through the Internet or through many online services The USENET contains more than 14,000 forums called newsgroups that cover every imaginable interest group. It is used daily by millions of people around the world. Proxy Servers Proxy servers sit between a client program typically a Web browser and an external server (typically another server on the Web) to filter requests, improve performance, and share connections. Telnet Servers A Telnet server enables users to log on to a host computer and perform tasks as if they're working on the remote computer itself. Web Servers At its core, a Web server serves static content to a Web browser by loading a file from a disk and serving it across the network to a user's Web browser. The browser and server talking to each other using HTTP mediate this entire exchange.

A TAP (Test Access Point) is a passive splitting mechanism installed between a 'device of interest' and the network. TAPs transmit both the send and receive data streams simultaneously on separate dedicated channels, ensuring all data arrives at the monitoring device in real time.

A network interface unit (NIU) (sometimes called a network interface device) is a device that serves as a common interface for various other devices within a local area network (LAN), or as an interface to allow networked computers to connect to an outside network.

A network server is a powerful computer connected to your business network.Network servers have many functions and can form an important part of your computernetwork. They are usually used for shared file storage and to run centralised applications, such as your customer database.

A network server is a computer system, which is used as the central repository of data and various programs that are shared by users in a network. If you have a computer that you're no longer using due to its slow speed, you can turn it into a network serverfor other computers in your household.

A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area networkand run multi-user operating systems.

A forwarder is a Domain Name System (DNS) server on a network that is used to forward DNS queries for external DNS names to DNSservers outside that network. You can also configure your server toforward queries according to specific domain names using conditional forwarders.

A fully qualified domain name (FQDN) is the complete domain name for a specific computer, or host, on the Internet. The FQDN consists of two parts: the hostname and the domain name. For example, an FQDNfor a hypothetical mail server might be mymail.somecollege.edu 

A Dynamic Host Configuration Protocol (DHCP) scope is the consecutive range of possible IP addresses that the DHCP server can lease to clients on a subnet. Scopes typically define a single physical subnet on your network to which DHCP services are offered.

The Lmhosts file is a local text file that maps Internet Protocol (IP) addresses to NetBIOS names of remote servers with which you want to communicate over the TCP/IP protocol. The Lmhosts file is located in the %SystemRoot%\System32\Drivers\Etc folder on a Windows computer.

Automatic Private IP Addressing (APIPA) is a feature of Windows-based operating systems (included in Windows 98, ME, 2000, and XP) that enables a computer to automatically assign itself an IP address when there is no Dynamic Host Configuration Protocol (DHCP) server available to perform that function. APIPA serves as a DHCP server failover mechanism and makes it easier to configure and support small local area networks (LANs).

If no DHCP server is currently available (either because the server is temporarily down or because none exists on the network), the computer selects an IP address from a range of addresses (from 169.254.0.0 - 169.254.255.255) reserved by the Internet Assigned Numbers Authority (IANA) for that purpose. The client uses Address Resolution Protocol (ARP) to ensure that the chosen address is not already being used by another network computer. Once the computer has assigned itself an IP address, it can communicate over TCP/IP with other computers on the LAN that are either configured for APIPA or are manually set to the correct address range and a subnet mask value of 255.255.0.0. APIPA is enabled by default, but can be disabled in some cases. DHCP messages notify the user when they are switched between DHCP addressing and APIPA.

A static IP address is an address that does not change over time unless changed manually. It is used when you need the IP address or network location to remain the same consistently. A good example of this is for a web server. If you go to www.google.com you are really going to the IP address of 66.102.7.99. If this were to change suddenly you would not be able to get to Google unless you knew the new IP address or until Google updated their DNS records. Most of the time your servers at work will use staitc IP addresses as well so you will always be able to access them and so that your network administrators will know how to get to them.

A Dynamic IP address is an address that keeps on changing. It is mostly used when having a consistent IP address is not necessary. An example of this would be the IP address your ISP (internet service provider) assigns you when you log on to the internet. You must have an IP address to surf the web but once you disconnect you loose that address. Then the next time you sign on you are assigned a new one. This is done usingDHCP. Your workstation at work most likely has a dynamic IP address since there is usually no need for it to have the same IP address all the time. Dynamic IP addresses are leased from the DHCP server for a period of time and then your computer will request a renewal or a new IP address when the lease expires.

Subnets provide a lot of benefits for network administrators, and ultimately users, by making administration and routing more efficient.

Prevents Unnecessary Broadcasts

• Computers connected to a network regularly send information to whichever computer is on their network, referred to as a broadcast. Broadcasts are caused by viruses and malware, as well as many legitimate programs. On smaller networks (e.g., fewer than 50 people), this may not pose a problem, but organizations with hundreds or thousands of users may quickly find their network slowed.

  Broadcasts, however, are not forwarded beyond a user's subnet. By dividing a larger IP address space into smaller subnets, you can stop broadcasts from affecting the whole physical network, and restrict them to the individual subnets.

Increases Security Options

• Most network security appliances work by evaluating traffic between networks. By putting sensitive resources on the same subnet as every other user, you make it more difficult to deploy security measures. Separating vital functions into subnets allows you to deploy security measures such as firewalls. Firewalls can be configured to ensure that only authorized hosts or other subnets gain access to these servers as well as other networks.

Simplifies Administration

• Oftentimes an organization has different departments that require access to different types of resources. If the accounting and janitorial departments are on the same subnet, for example, then their access restrictions have to be controlled on a host-by-host basis. But when the two departments are placed on separate subnets, then security options can be applied based on those subnetworks.

Controls Growth

• When planning a network, you can control the number of subnet masks available and how many hosts will be available for each subnet. For example, 192.168.1.0 with a subnet mask of 255.255.255.0 allows eight bits to be used to define the hosts (2 ^ 8 = 256, minus network and broadcast addresses, for a total of 254 potential hosts), but provides for over 16 million networks (2 ^ 24). A subnet mask of 255.255.0.0, however, would allow for over 65,000 networks and hosts each. With a little bit of planning, administrators can scale their subnets in a way that matches the number of networks anticipated to the number of hosts expected in each subnet.

An IP address is considered public if the IP number is valid and falls outside any of the IP address ranges reserved for private uses by Internet standards groups. (See private IP addresses)

Public IP addresses are used by Internet servers including those for Web sites and DNS servers), network routers or any computer connected directly to the Internet via a modem.

Each public IP is assigned to a range or block of addresses. The Internet Assigned Numbers Authority (IANA) controls ownership of these IP ranges and assigns each block to organizations such as Internet Service Providers (ISPs) who in turn allocate individual IP addreses to customers.

You’ll need to access the Disk Management tool from within Windows to do this. 

Open the Computer Management tool. Open the Start menu. Type “Computer Management” in the search bar of the Start menu and press enter.

Select the Disk Management tool. Click on Disk Management on the left side of the window and you should see all of the disks and their partitions on your computer.

Create a new volume. You should now see a new unlocated partition in your Disk Management window. Right-click on the unallocated partition and select the New Simple Volume option.

The New Simple Volume Wizard. The New Simple Volume Wizard should popup. Click on the Next button to continue.

Enter size of new partition. Enter the amount of memory you wish to allocate for your new partition and click on the Next button.

• Note: You cannot make your new volume larger than the maximum amount of memory available.

Give the new volume a letter name or path. Select from the menu, a letter name for your new partition and click on the “Next” button.

• The letter name or path is used by Windows to identify and navigate to your new volume.

Settings for the new volume.

• Click on the Format this volume with the following settings:
• For File System, select NTFS
• For Allocation unit size, select Default
• For Volume Label, type the name you wish to give your new drive.
• Click on the Perform a quick format
• Then click on the Next button

Create the new volume. Look over your settings and click on the Finish button.

Format the new volume.

• You will get a popup asking you to partition your new drive. Click on the Format disk button.
• A new window will popup. Keep the settings and click on the Start button.
• A warning will popup. Click on the OK button.

Check new volume. If everything was done correctly, you should now see your new drive in the Disk Management window.

1.  Click on Start and select Run.

2.  In the Run window, type cmd and click OK.

3.  In the next window, type ipconfig/all and press the Enter key.

4.  Look under Ethernet adapter Local Area Connection or Wireless Connection for the IP Address.

Old PC's used 25 pin connectors but only about 9 pins were actually used so later on most connectors were only 9-pin. Each of the 9 pins usually connects to a wire. Besides the two wires used for transmitting and receiving data, another pin (wire) is signal ground. The voltage on any wire is measured with respect to this ground. Thus the minimum number of wires to use for 2-way transmission of data is 3. Except that it has been known to work with no signal ground wire but with degraded performance and sometimes with errors.

Straight Cable Usually use straight cable to connect different type of devices. This type of cable will be used most of the time and can be used to: 1) Connect a computer to a switch/hub's normal port. 2) Connect a computer to a cable/DSL modem's LAN port. 3) Connect a router's WAN port to a cable/DSL modem's LAN port. 4) Connect a router's LAN port to a switch/hub's uplink port. (Normally used for expanding network) 5) Connect two switches/hubs with one of the switch/hub using an uplink port and the other one using normal port. If you need to check how straight cable looks like, it's easy. Both sides (side A and side B) of cable have wire arrangement with same color. Crossover Cable Sometimes you will use crossover cable, it's usually used to connect same type of devices. A crossover cable can be used to: 1) Connect two computers directly. 2) Connect a router's LAN port to a switch/hub's normal port. (Normally used for expanding network) 3) Connect two switches/hubs by using normal port in both switches/hubs.

Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system (AS). It is defined as OSPF Version 2 in RFC 2328 (1998) for IPv4.

Piggybacking is a bi-directional data transmission technique in thenetwork layer (OSI model). It makes the most of the sent data frames from receiver to emitter, adding the confirmation that the data frame sent by the sender was received successfully (ACK acknowledge).

DEFINITION

Serial Line Internet Protocol (SLIP)

Posted by: Margaret Rouse

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SLIP is a TCP/IP protocol used for communication between two machines that are previously configured for communication with each other. For example, your Internet server provider may provide you with a SLIP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. Your dial-up connection to the server is typically on a slower serial line rather than on the parallel or multiplex lines such as a line of the network you are hooking up to.

Proxy ARP is a technique by which a device on a given network answers the ARP queries for a network address that is not on that network. The ARP Proxy is aware of the location of the traffic's destination, and offers its own MAC address as (ostensibly final) destination.

A network virtual terminal is a responsible of a basic terminal and provides a standard that the computer on either end of a telnet connection are assumed to follow. It defines how data and commands are send across the network. It allows interoperability between telnet and a variety of heterogenus components. 

The Gateway-to-Gateway Protocol (GGP) is an obsolete protocoldefined for routing datagrams between Internet gateways. TheGateway-to-Gateway Protocol was designed as an Internet Protocol(IP) datagram service similar to the Transmission Control Protocol(TCP) and the User Datagram Protocol (UDP).

Exterior Gateway Protocol (EGP) is a protocol for exchanging routing information between two neighbor gateway hosts (each with its own router) in a network of autonomous systems. EGP is commonly used between hosts on the Internet to exchange routing table information.

Traffic shaping, also known as packet shaping, Quality of Service (QoS) or bandwidth management, is the manipulation and prioritization of network traffic to reduce the impact of heavy users or machines from effecting other users.

In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model.

Baseband is type of transmission that is using current to send signal over the wire as digital wave. It can transmit only one signal at a time, due to requirement of the exclusive use of the wire. This type of transmission is allowing only on device to transmit in the network at one time, while other devices need to wait for the end of transmission.

While in some cases baseband supports full-duplexing, in most cases the half-duplexing is used for sending signals upstream and downstream.

Ethernet is using baseband for LANs. If the data is needed to be send to a server, network interface card is making request to use the wire. While the wire is busy, NIC retries its request. When the wire is available, the data is being sent. The process takes milliseconds and is not noticeable by user.

Broadband is using analog signal that is modulated. It is used to transmit cable TV to premises. Broadband is using different frequencies which increases amount of data it can carry at one time. The amount of data is higher 25 times compared to the baseband. Usually broadband is transmitting data in one direction, towards user. If user needs to send data, an individual channel is used for data and special amplifiers are used for data separation. While broadband signal can travel longer distances it is having additional expenses due to the use of extra equipment.

1. Ring Topology 2. Star Topology. 3. Bus Topology. 4. Mess Topology. 5. Hybrid Topology. 

The differences between FTP and TFTP:

•  FTP is connection oriented, where as TFTP is not.
•  TFTP uses error checking and flow control, where as TFTP does not cause error checking.
•  FTP uses TCP as transport protocol, where as TFTP uses UDP as transport protocol.
•  Authentication is mandatory in FTP, where as authentication is not needed in TFTP. 
•  Just getting and putting application effectively is the design concern of TFTP, where as FTP provides more control and data connection aspects.

The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.

Difference between ARP and RARP:

The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.  The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.

The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.

The Internet Control Message Protocol (ICMP) is one of the main protocols of the internet protocol suite. It is used by network devices, like routers, to send error messages indicating, for example, that a requested service is not available or that a host or router could not be reached.

Repeater: Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link. Bridges:  These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion. Routers: They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission. Gateways: They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.

In telecommunications, the term protocol data unit (PDU) has the following meanings: Information that is delivered as a unit among peer entities of a network and that may contain control information, such as address information, or user data.

Project 802 is a set of networking standards and procedures for implementing networks, and creating network related equipment. As long as manufacturers of networking equipment follow the same standards, then interoperability and compatibility across multiple platforms and network systems will remain high. The IEEE (institute of Electrical and Electronics Engineers) designed Project 802 and it became a standard in 1983. 802 actually stands for the date of Project 802’s inception, which was February of 1980, hence 802. The project mostly covers physical media aspects of networking, such as cabling, attachments, hardware recommendations, and some logical networking aspects as well.

Data is represented by computers and other telecommunication devices using signals. Signals are transmitted in the form of electromagnetic energy from one device to another. Electromagnetic signals travel through vacuum, air or other transmission mediums to travel between one point to another(from source to receiver).

Electromagnetic energy (includes electrical and magnetic fields) includes power, voice, visible light, radio waves, ultraviolet light, gamma rays etc.

Transmission medium is the means through which we send our data from one place to another. The first layer (physical layer) of Communication Networks OSI Seven layer model is dedicated to the transmission media, we will study the OSI Model later.

Wired or Guided Media or Bound Transmission Media: Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable. Each of them has its own characteristics like transmission speed, effect of noise, physical appearance, cost etc.

Wireless or Unguided Media or Unbound Transmission Media: Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. This type of transmission is called Wireless communication. Nowadays wireless communication is becoming popular. Wireless LANs are being installed in office and college campuses. This transmission uses Microwave, Radio wave, Infra red are some of popular unbound transmission media.

Bit rate is a measure of the number of data bits (that's 0's and 1's) transmitted in one second. A figure of 2400 bits per second means 2400 zeros or ones can be transmitted in one second, hence the abbreviation 'bps'. Baud rate by definition means the number of times a signal in a communications channel changes state.

A media access control address (MAC address), also called physical address, is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet and WiFi.

A gateway acts as a conversion from one protocol to another or in the case of Voice over IP (VoIP) from the VoIP network to the POTS network. A router works by looking at the IP address in the data packet and decides if it is for internal use or if the packet should move outside the network (to the WAN).

When the computers on the network simply listen and receive the signal, they are referred to as passive because they don't amplify the signal in any way. Example for passive topology - linear bus.

Network Basic Input Output System provides session layer of OSI model related services which allows the applications on different computers for communicating over a LAN. NetBIOS runs over TCP/IP through NetBIOS over TCP/IP (NBT) protocol. This process results in every computer in the network with NetBIOS name and an IP address that corresponds to a host name. NetBIOS Extended User Interface is an extended version of NetBIOS. It is a program that allows computers to communicate within a local area network. NetBEUI forms the frame format which was not a specification of NetBIOS. NetBEUI is the best choice for performing communication within a LAN.

Frame relay is a packet switching technology. It will operate in the data link layer.

The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"

possible ways of data exchange

(i) Simplex  

(ii) Half-duplex  

(iii) Full-duplex.

 Physical movement of information and concerning about bit priority, synchronization, clock etc is referred as transmission, where as full exchange of information among media of communication is referred as communication. Transmission is all about transmitting of data to the destination, where as the dialogue between the source and destination is all about communication.

A subnet (short for "subnetwork") is an identifiably separate part of an organization's network. Typically, a subnet may represent all the machines at one geographic location, in one building, or on the same local area network (LAN). Having an organization's network divided into subnets allows it to be connected to the Internet with a single shared network address. Without subnets, an organization could get multiple connections to the Internet, one for each of its physically separate subnetworks, but this would require an unnecessary use of the limited number of network numbers the Internet has to assign. It would also require that Internet routing tables on gateways outside the organization would need to know about and have to manage routing that could and should be handled within an organization.

Broadband :In this type .Every host sends the packet/message to all the host. the message has a source address and a destination address. destination address helps the host to identify whether the message is indeed for them or somebody else the source address allows them to identify from whom the message has come. Point to Point :In this type of technology there are multiple connections (transmission lines) between 2 hosts. so the the packet can take different routes if a particular route is congested.

Sliding window is a technique for controlling transmitted data packets between two network computers where reliable and sequential delivery of data packets is required, such as when using the Data Link Layer (OSI model) or Transmission Control Protocol (TCP).

A technique used in advanced microprocessors where the microprocessor begins executing a second instruction before the first has been completed. That is, several instructions are in the pipelinesimultaneously, each at a different processing stage.

The pipeline is divided into segments and each segment can execute its operation concurrently with the other segments. When a segment completes an operation, it passes the result to the next segment in the pipeline and fetches the next operation from the preceding segment. The final results of each instruction emerge at the end of the pipeline in rapid succession.

Although formerly a feature only of high-performance and RISC -based microprocessors, pipelining is now common in microprocessors used in personal computers. Intel's Pentium chip, for example, uses pipelining to execute as many as six instructions simultaneously.

Pipelining is also called pipeline processing.

A similar technique used in DRAM, in which the memory loads the requested memory contents into a smallcache composed of SRAM and then immediately begins fetching the next memory contents. This creates a two-stage pipeline, where data is read from or written to SRAM in one stage, and data is read from or written to memory in the other stage.

DRAM pipelining is usually combined with another performance technique called burst mode. The two techniques together are called a pipeline burst cache.

It is the simplest kind of automatic repeat-request (ARQ) method. Astop-and-wait ARQ sender sends one frame at a time; it is a special case of the general sliding window protocol with both transmit and receive window sizes equal to 1 and more than one respectively .

Automatic repeat request (ARQ) is a protocol for error control in data transmission. When the receiver detects an error in a packet, it automatically requests the transmitter to resend the packet. This process is repeated until the packet is error free or the error continues beyond a predetermined number of transmissions. ARQ is sometimes used with Global System for Mobile (GSM) communication to guarantee data integrity.

* Flow control: adjust and confirm data flow rate for successful transmission. * Error Control: a way to recover corrupted data .

Bit stuffing is the insertion of one or more bits into a transmission unit as a way to provide signaling information to a receiver. The receiver knows how to detect and remove or disregard the stuffed bits.

Same idea as bit-stuffing, but operates on bytes instead of bits.

Use reserved characters to indicate the start and end of a frame. For instance, use the two-character sequence DLE STX (Data-Link Escape, Start of TeXt) to signal the beginning of a frame, and the sequence DLE ETX (End of TeXt) to flag the frame's end.

Problem: What happens if the two-character sequence DLE ETX happens to appear in the frame itself?

Solution: Use character stuffing; within the frame, replace every occurrence of DLE with the two-character sequence DLE DLE. The receiver reverses the processes, replacing every occurrence of DLE DLE with a single DLE.

In fixed-size framing, there is no need for defining the boundaries of the frames. The size itself can be used as a delimiter.

The bits to be is first broken into discrete frames at the data link layer. In order to guarantee that the bit stream is error free, the checksum of each frame is computed. When a frame is received, the data link there, recomputes the checksum. If it is different from the checksum present in the frame, then the data link layer knows that an error has occurred. It then discards the bad frame and sends back a request for-retransmission. Breaking the bit stream into frames is called as framing.

ENCODER- a digital circuit that produces a binary output code depending on which of its inputs are activated.

DECODER- a digital circuit that converts an input binary code into a single numeric output. A BCD number is a four-bit binary group that represents one of the ten decimal digits 0 through 9.

In a (n,k) linear block code:1st portion of k bits is always identical to the message sequence to be transmitted.2nd portion of (n-k ) bits are computed from message bits according to the encoding rule and is called parity bits.

In coding theory, a linear code is an error-correcting code for which any linear combination of codewords is also a codeword. Linear codes are traditionally partitioned into block codesand convolutional codes, although turbo codes can be seen as a hybrid of these two types.

Forward error correction (FEC) is a method of obtaining error control in data transmission in which the source (transmitter) sends redundant data and the destination (receiver) recognizes only the portion of the data that contains no apparent errors.

Data Link Layer Protocols

The data link layer provides service to the Network Layer above it:

• The network layer is interested in getting messages to the corresponding network layer module on an adjacent machine.
• The remote Network Layer peer should receive the identical message generated by the sender (e.g., if the data link layer adds control information, the header information must be removed before the message is passed to the Network Layer).
• The Network Layer wants to be sure that all messages it sends, will be delivered correctly (e.g., none lost, no corruption). Note that arbitrary errors may result in the loss of both data and control frames.
• The Network Layer wants messages to be delivered to the remote peer in the exact same order as they are sent.

Note: It is not always clear that we really want our data link layer protocol to provide this type of service. What if we run real-time applications across the link?

Nonetheless, the ISO reference model suggests that the data link layer provide such a service, and we now examine the protocols that provide such a service

Examples of the Data Link Layer

High-level Data Link Control

Adopted as part of X.25.

• Bit oriented (uses bit stuffing and bit delimeters)
• 3-bit sequence numbers
• up to 7 unack'ed frames can be outstanding at any time (how big is the receiver's window? one)
• ACK's the ``frame expected'' rather than last frame received (any difference between the two? No, as long as same convention).

Basically, Go Back N protocol.

In communications, error detection refers to a class of techniques fordetecting garbled messages. Two of the simplest and most common techniques are called checksum and CRC.

•How to detect errors

If only data is transmitted, errors cannot be detected 

Send more information with data that satisfies a special relationship

 Add redundancy

• Vertical Redundancy Check (VRC)

• Longitudinal Redundancy Check (LRC)

• Cyclic Redundancy Check

Signals are usually transmitted over some transmission media that are broadly classified in to two categories

.Guided Media:These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.

Unguided Media: This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.

a. Cables

b. Leased Lines

c. Last-Mile Links

d. Wireless Links

Network Layer

Network layer is responsible for providing logical address know as IP address. Router works on this layer. Main functions of this layer are following :-

• Define IP address
• Find routes based on IP address to reach its destination
• Connect different data link type together like as Token Ring, Serial, FDDI, Ethernet etc.

Transport Layer

• It sets up and maintain the connection between two devices.
• It multiplexes connections that allow multiple applications to simultaneously send and receive data.
• According to requirement data transmit method can be connection oriented or connection less.
• For unreliable data delivery connection less method is used.
• Connection less methods use UDP protocol.
• For reliable data delivery connection oriented method is used.
• Connection oriented methods use TCP protocol.
• When Implemented a reliable connection, sequence numbers and acknowledgments (ACKs) are used.
• Reliable connection controls flow through the use of windowing or acknowledgements.

The Session Layer

Session layer deals with connections. It establishes, manages, and terminates sessions between two communicating node. This layer provides its services to the presentation layer. Session layer also synchronizes dialogue between the presentation layers of the two hosts and manages their data exchange. For example, web servers may have many users communicating with server at a given time. Therefore, keeping track of which user communicates on which path is important and session layer handle this responsibility accurately.

The data link layer is also responsible for logical link control, media access control, hardware addressing, error detection and handling and defining physical layer standards. It provides reliable data transfer by transmitting packets with the necessary synchronization, error control and flow control.

Physical characteristics of interface and media

Representation of bits/encoding

Data rate / transmition ratesynchronization of bits

Line confurationphysical topologyTransmission mode.

Transport Layer

Physical, data link and network layers are network support layers and session, presentation and application layers are user support layers.

The seven Open Systems Interconnection layers are:

Layer 7: The application layer. This is the layer at which communication partners are identified (Is there someone to talk to?), network capacity is assessed (Will the network let me talk to them right now?), and that creates a thing to send or opens the thing received.  (This layer is not the application itself, it is the set of services an application should be able to make use of directly, although some applications may perform application layer functions.)

Layer 6: The presentation layer. This layer is usually part of an operating system (OS) and converts incoming and outgoing data from one presentation format to another (for example, from clear text to encrypted text at one end and back to clear text at the other).

Layer 5: The session layer. This layer sets up, coordinates and terminates conversations. Services include authentication and reconnection after an interruption. On the Internet,Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) provide these services for most applications.

Layer 4: The transport layer. This layer manages packetization of data, then the delivery of the packets, including checking for errors in the data once it arrives. On the Internet, TCP and UDP provide these services for most applications as well.

Layer 3: The network layer. This layer handles the addressing and routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). IP is the network layer for the Internet.

Layer 2: The data-link layer. This layer sets up links across the physical network, putting packets into network frames. This layer has two sub-layers, the Logical Link Control Layer and the Media Access Control Layer. Ethernet is the main data link layer in use.

Layer 1: The physical layer. This layer conveys the bit stream through the network at the electrical, optical or radio level. It provides the hardware means of sending and receiving data on a carrier network.

Time-division multiplexing (TDM) is a method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration. Each individual data stream is reassembled at the receiving end based on the timing.

Different type of multiplexing is used in communication the following three major multiplexing techniques are:

• Frequency division multiplexing
• Wavelength division multiplexing
• Time division multiplexing

Unicast: A term used in communication to describe a piece of information to send from one point to another. There are only sender and receiver. All LANs support unicast transfer mode and most applications that employ TCP transport protocol uses unicast messaging. Broadcast: A term used for describing communication that is sent a piece of information from one point to all other points. There is one sender and multiple receivers. All LANs support broadcast transmission.  Multicast: A term described in communicating a piece of information sent from one or more points to a set of other points. The senders and receivers are one or more.

The semantic gap characterizes the difference between two descriptions of an object by different linguistic representations, for instance languages or symbols. According to Hein, the semantic gapcan be defined as "the difference in meaning between constructs formed within different representation systems".

Routing is the process of selecting best paths in a network. In the past, the term routing also meant forwarding network traffic among networks. However, that latter function is better described as forwarding. Routing is performed for many kinds of networks, including the telephone network (circuit switching), electronic data networks (such as theInternet), and transportation networks.

Latency:

Latency = delay. It’s the amount of delay (or time) it takes to send information from one point to the next. Latency is usually measured in milliseconds or ms. It’s also referred to (during speed tests) as a ping rate.Latency is delay. For our purposes, it is the amount of time it takes a packet to travel from source to destination. Together, latency and bandwidth define the speed and capacity of a network. Latency is normally expressed in milliseconds. One of the most common methods to measure latency is the utility ping. A small packet of data, typically 32 bytes, is sent to a host and the RTT (round-trip time, time it takes for the packet to leave the source host, travel to the destination host and return back to the source host) is measured.

Bandwidth:

Bandwidth is normally expressed in bits per second. It's the amount of data that can be transferred during a second. Solving bandwidth is easier than solving latency. To solve bandwidth, more pipes are added. For example, in early analog modems it was possible to increase bandwidth by bonding two or more modems. In fact, ISDN achieves 128K of bandwidth by bonding two 64K channels using a datalink protocol called multilink-ppp. Bandwidth and latency are connected. If the bandwidth is saturated then congestion occurs and latency is increased. However, if the bandwidth of a circuit is not at peak, the latency will not decrease. Bandwidth can always be increased but latency cannot be decreased. Latency is the function of the electrical characteristics of the circuit.

a. Connectivity  b. Cost-effective Resource Sharing  c. Support for common Services  d. Performance

Latency: Think of latency as the speed limit on a highway. Traffic speed on a motorway is affected by many variables such as weather, other traffic, and highway signs. Likewise, data packets traversing a network are affected by many variables as well. The first step in mitigating latency is to break down the overall latency into that due to the network and that due to the application and its associated servers. With that determination made, visually graph both the application and network latency to help identify patterns and anomalies that deserve closer attention so that you can later drill down and figure out exactly what is causing the bottleneck.

Throughput: Throughput is the amount of traffic a network can carry at any one time. Like the analogy of traffic used to explain latency above, think of throughput as analogous to the number of lanes on a highway. The more lanes, the more traffic a highway can accommodate. When thinking of networks, the higher the bit rate, the faster files transfer. Slow response times might be an issue with your network not having enough throughput.

Packet Loss: Glitches, errors, or network overloading might result in the loss of data packets. Sometimes routers or switches might shed traffic intentionally to maintain overall network performance or to enforce a particular service level. In a well-tuned network intentional packet loss is hopefully a rare occurrence, though packet loss is still something that happens regularly due to a host of other reasons, and must be monitored closely to ensure overall network performance.

Retransmission: When packet loss does occur, those lost packets are retransmitted. This retransmission process can cause two delays; one from re-sending the data and the second delay resulting from waiting until the data is received in the correct order before forwarding it up the protocol stack.

Latency: Think of latency as the speed limit on a highway. Traffic speed on a motorway is affected by many variables such as weather, other traffic, and highway signs. Likewise, data packets traversing a network are affected by many variables as well. The first step in mitigating latency is to break down the overall latency into that due to the network and that due to the application and its associated servers. With that determination made, visually graph both the application and network latency to help identify patterns and anomalies that deserve closer attention so that you can later drill down and figure out exactly what is causing the bottleneck.

Throughput: Throughput is the amount of traffic a network can carry at any one time. Like the analogy of traffic used to explain latency above, think of throughput as analogous to the number of lanes on a highway. The more lanes, the more traffic a highway can accommodate. When thinking of networks, the higher the bit rate, the faster files transfer. Slow response times might be an issue with your network not having enough throughput.

Packet Loss: Glitches, errors, or network overloading might result in the loss of data packets. Sometimes routers or switches might shed traffic intentionally to maintain overall network performance or to enforce a particular service level. In a well-tuned network intentional packet loss is hopefully a rare occurrence, though packet loss is still something that happens regularly due to a host of other reasons, and must be monitored closely to ensure overall network performance.

Retransmission: When packet loss does occur, those lost packets are retransmitted. This retransmission process can cause two delays; one from re-sending the data and the second delay resulting from waiting until the data is received in the correct order before forwarding it up the protocol stack.

Advantages of Distributed Processing

a. Security/Encapsulation

b. Distributed database

c. Faster Problem solving

d. Security through redundancy

e. Collaborative Processing

Advantages of Distributed Data Processing

• Lower Cost

Larger organizations invest in expensive mainframe and supercomputers to function as centralized servers. Each mainframe machine, for example, costs several hundred thousand dollars versus several thousand dollars for a few minicomputers, according to the University of New Mexico. Distributed data processing considerably lowers the cost of data sharing and networking across an organization by comprising several minicomputers that cost significantly less than mainframe machines.

• Reliable

Hardware glitches and software anomalies can cause single-server processing to malfunction and fail, resulting in a complete system breakdown. Distributed data processing is more reliable, since multiple control centers are spread across different machines. A glitch in any one machine does not impact the network, since another machine takes over its processing capability. Faulty machines are quickly isolated and repaired. This makes distributed data processing more reliable than single-server processing systems.

• Improved Performance and Reduced Processing Time

Single computers are limited in their performance and efficiency. An easy way to increase performance is by adding another computer to a network. Adding yet another computer will further augment performance, and so on. Distributed data processing works on this principle and holds that a job gets done faster if multiple machines are handling it in parallel, or synchronously. Complicated statistical problems, for example, are broken into modules and allocated to different machines where they are processed simultaneously. This significantly reduces processing time and improves performance.

• Flexible

Individual computers that comprise a distributed network are present at different geographical locations. For example, an organizational-distributed network comprising of three computers can have each machine in a different branch. The three machines are interconnected via the Internet and are able to process data in parallel, even while at different locations. This makes distributed data-processing networks more flexible. The system is flexible also in terms of increasing or decreasing processing power. For example, adding more nodes or computers to the network increases processing power and overall system capability, while reducing computers from the network decreases processing power.

Multiple access is a radio transmission scheme that allows several earth stations to transmit in the same time span. This provides the way to network these stations together, either in a Star or a Mesh network. 

Typically in a TCP/IP network, nodes such as servers, workstations and network devices each have a defined default route setting, (pointing to the default gateway), defining where to send packets for IP addresses for which they can determine no specific route. The gateway is by definition a router.

(1) In networks, a processing location. A node can be a computer or some other device, such as a printer. Every node has a unique network address, sometimes called a Data Link Control (DLC) address or Media Access Control (MAC) address.

(2) In tree structures, a point where two or more lines meet.

A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users.

The most common resource shared today is connection to the Internet. Other shared resources can include a printer or a file server.

It is possible that a switch receives packets faster than the shared link can accommodate and stores in its memory, for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped and in this state is said to congested state.

Kerberos is a secure method for authenticating a request for a service in a computer network. Kerberos was developed in the Athena Project at the Massachusetts Institute of Technology (MIT). The name is taken from Greek mythology; Kerberos was a three-headed dog who guarded the gates of Hades.

An mrouter, or multicast router, is a router program that distinguishes between multicast and unicast packets and determines how they should be distributed along the Multicast Internet (sometimes known as the Multicast Backbone or MBone).

Traffic shaping, also known as packet shaping, Quality of Service (QoS) or bandwidth management, is the manipulation and prioritization of network traffic to reduce the impact of heavy users or machines from effecting other users.

Packet filtering is a firewall technique used to control network access by monitoring outgoing and incoming packets and allowing them to pass or halt based on the source and destination Internet Protocol (IP) addresses, protocols and ports.

Baseband:  - Digital signals are used - Frequency division multiplexing is not possible - Baseband is bi-directional transmission - Short distance signal travelling - Entire bandwidth of the cable is consumed by a single signal in a baseband transmission. Broadband: - Analog signals are used - Transmission of data is unidirectional - Signal travelling distance is long - Frequency division multiplexing is possible - The signals are sent on multiple frequencies and allow all the multiple signals are sent simultaneously in broadband transmission.

A mesh network is a network topology in which each node relays data for the network. All mesh nodes cooperate in the distribution of data in the network.Mesh networks can relay messages using either a flooding technique or a routing technique.

1. Ring Topology  2. Star Topology.  3. Bus Topology.  4. Mess Topology.  5. Hybrid Topology.

Server-based network. Peer-to-peer network. Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources. Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration.

The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes. 

The differences between ARP and RARP: - Address Resolution Protocol is utilized for mapping IP network address to the hardware address that uses data link protocol.  - Reverse Address Resolution Protocol is a protocol using which a physical machine in a LAN could request to find its IP address from ARP table or cache from a gateway server.  - IP address of destination to physical address conversion is done by ARP, by broadcasting in LAN. - Physical address of source to IP address conversion is done by RARP.  - ARP associates 32 bit IP address with 48 bit physical address. - Allowing a host to discover its internet address after knowing only its physical address is done by RARP.

NetBIOS Extended User Interface (NetBEUI) This is a separate protocol from NetBIOS. It supports small to medium networks providing transport and network layer support. It is fast and small and works well for the DOS operating system but NetBEUI is not a routable protocol.

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) provides a way of storing the same data in different places (thus, redundantly) on multiple hard disks (though not all RAID levels provide redundancy). By placing data on multiple disks, input/output (I/O) operations can overlap in a balanced way, improving performance. Since multiple disks increase the mean time between failures (MTBF), storing data redundantly also increases fault tolerance.

The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.

The Web, or World Wide Web, is basically a system of Internet servers that support specially formatted documents. The documents are formatted in a markup language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files.

The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems.HTTP is the foundation of data communication for the World Wide Web. Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text.

Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely. On the Web, HTTP and FTP protocols allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific application and data on that computer.

The client–server model of computing is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients.

Time-division multiplexing (TDM) is a method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration. Each individual data stream is reassembled at the receiving end based on the timing.

Wavelength-division multiplexing (WDM) is a method of combining multiple signals on laser beams at various infared (IR) wavelengths for transmission along fiber optic media. Each laser is modulated by an independent set of signals.

Frequency-division multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel.

The Internet Control Message Protocol (ICMP) is one of the main protocols of the internet protocol suite. It is used by network devices, like routers, to send error messages indicating, for example, that a requested service is not available or that a host or router could not be reached.

 A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a local area network (LAN) by dividing it into two segments.

Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destinationMAC addresses, and sometimes the frame size - in making individual forwarding decisions.

Bridges serve a similar function as network switches that also operate at Layer 2. Traditional bridges, though, support one network boundary (accessible through ahardware port), whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.

A repeater is a network device that retransmits a received signal with more power and to an extended geographical or topological network boundary than what would be capable with the original signal.

An IP address, or simply an "IP," is a unique address that identifies a device on theInternet or a local network. It allows a system to be recognized by other systems connected via the Internet protocol.

At its most basic, Bluetooth could be used for transferring files or contact details between two phones for example, or for an ongoing transfer of data, such as in a hands free kit, where the earpiece woulduse Bluetooth to wirelessly send and receive sound to and from a phone.

Carrier Sense Multiple Access (CSMA) is a network protocol that listens to or senses network signals on the carrier/medium before transmitting any data. CSMA is implemented in Ethernet networks with more than one computer or network device attached to it. CSMA is part of the Media Access Control (MAC) protocol.

NCP connected processes running on different ARPANET computers. Protocols on the ARPANET in the physical layer, data link layer and network layer were implemented on separate interface massage processors. This meant that NCP acted much like a transport layer, as it defined the procedure for connecting two hosts. The switch to TCP/IP in 1983 marked a major move toward the modern Internet. TCP/IP remains the standard protocol of online communication.

In telecommunication, Hamming codes are a family of linear error-correcting codes that generalize the Hamming(7,4)-code, and were invented by Richard Hamming in 1950.Hamming codes can detect up to two-bit errors or correct one-bit errors without detection of uncorrected errors.

Redundancy is a system design in which a component is duplicated so if it fails there will be a backup. 

Redundancy has a negative connotation when the duplication is unnecessary or is simply the result of poor planning.

• Single bit error

  In a frame, there is only one bit, anywhere though, which is corrupt.

• Multiple bits error

  Frame is received with more than one bits in corrupted state.

• Burst error

  Frame contains more than1 consecutive bits corrupted.

The data link layer is responsible for logical link control, media access control, hardware addressing, error detection and handlingand defining physical layer standards. It provides reliable data transferby transmitting packets with the necessary synchronization, error control and flow control.

Types of Transmission Media

Transmission media is broadly classified into two groups.

1. Wired or Guided Media or Bound Transmission Media

2. Wireless or Unguided Media or Unbound Transmission Media

• Frequency division multiplexing
• Wavelength division multiplexing
• Time division multiplexing

Synchronous transmission is transmission of signals in a fixed interval based on a predefined clocking signal and is meant for constant and reliable transmission of time-sensitive data such as VoIP and audio/video streaming. 

This method of transmission is used when large amounts of data need to be transferred quickly since data is transferred in large blocks instead of individual characters. The data blocks are spaced and grouped in regular intervals and preceded by synchronous characters that a remote device decode and use to synchronize the connection between the end points. 

After synchronization is complete, the transmission can begin. 

Asynchronous transmission is the transmission of data in which each character is a self-contained unit with its own start and stop bits and an uneven interval between them.

Asynchronous transmission is also referred to as start/stop transmission.

(1) Sampling is the key technique used to digitize analog information. For example, music CDs are produced by sampling live sound at frequent intervals and then digitizing each sample. The termsampling is also used to describe a similar process in digitalphotography.

(2) A technique used to capture continuous phenomena, whereby periodic snapshots are taken. If the sampling rate is fast enough, the human sensory organs cannot discern the gaps between each snapshot when they are played back. This is the principle behind motion pictures.

Refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once. In contrast, a walkie-talkie is a half-duplex device because only one party can transmit at a time.

Half-duplex is a type of communication in which data can flow back and forth between two devices, but not simultaneously. Each device in a half-duplex system can send and receive data, but only one device can transmit at a time.

An example of a half-duplex device is a CB (citizens band) radio. The CB protocol, which is used by truckers, police officers, and other mobile personnel, allows users to communicate back and forth on a specific radio frequency.

Simplex is a communications mode in which only one signal is transmitted, and it always goes in the same direction. The transmitter and the receiver operate on the same frequency.

Multiplexing is a popular networking technique that integrates multiple analog and digital signals into a signal transmitted over a shared medium. Multiplexers and de-multiplexers are used to convert multiple signals into one signal.

A media access control address (MAC address), also called physical address, is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet and WiFi.

A portion of a network that shares a common address component. On TCP/IP networks, subnets are defined as all devices whose IP addresses have the same prefix. For example, all devices with IP addresses that start with 100.100.100. would be part of the same subnet. Dividing a network into subnets is useful for both security and performance reasons. IP networks are divided using a subnet mask.

The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols, which employs the hop count as a routingmetric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15.

Bandwidth describes the maximum data transfer rate of a network or Internetconnection. It measures how much data can be sent over a specific connection in a given amount of time.

(i) Broadcast (ii) point-to-point.

Piggybacking, in a wireless communications context, is the unauthorized access of a wireless LAN.  Piggybacking is sometimes referred to as "Wi-Fi squatting." 

The usual purpose of piggybacking is simply to gain free network access rather than any malicious intent, but it can slow down data transfer for legitimate users of the network. Furthermore, a network that is vulnerable to piggybacking for network access is equally vulnerable when the purpose is data theft, dissemination of viruses, or some other illicit activity. 

Protocol pipelining is a technique in which multiple requests are written out to a single socket without waiting for the corresponding responses. Pipelining can be used in various application layer network protocols, like HTTP/1.1, SMTP and FTP.

In telecommunications, the round-trip delay time (RTD) or round-trip time (RTT) is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. This time delay therefore consists of the propagation timesbetween the two points of a signal.

Typically in a TCP/IP network, nodes such as servers, workstations and network devices each have a defined default route setting, (pointing to the default gateway), defining where to send packets for IP addresses for which they can determine no specific route. The gateway is by definition a router.

In communication networks, a node (Latin nodus, 'knot') is either a connection point, a redistribution point, or a communication endpoint (e.g. data terminal equipment). The definition of a node depends on thenetwork and protocol layer referred to.

A network protocol defines rules and conventions for communication between network devices. Protocols forcomputer networking all generally use packet switching techniques to send and receive messages in the form of packets.

Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged into messages sent and received.

Some protocols also support message acknowledgement and data compression designed for reliable and/or high-performance network communication. Hundreds of different computer network protocols have been developed each designed for specific purposes and environments.

A network protocol defines rules and conventions for communication between network devices. Protocols forcomputer networking all generally use packet switching techniques to send and receive messages in the form of packets.

Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged into messages sent and received.

Some protocols also support message acknowledgement and data compression designed for reliable and/or high-performance network communication. Hundreds of different computer network protocols have been developed each designed for specific purposes and environments.

When you have two or more computers connected to each other, you have a network. The purpose of a network is to enable the sharing of files and information between multiple systems. The Internet could be described as a global network of networks. Computer networks can be connected through cables, such as Ethernet cables or phone lines, or wirelessly, using wireless networking cards that send and receive data through the air.

In computer networking, source routing, also called path addressing, allows a sender of a packet to partially or completely specify the routethe packet takes through the network. In contrast, in non-source routing protocols, routers in the network determine the path based on the packet's destination.

The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routingmetric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination.

The Serial Line Internet Protocol (also SLIP) is an encapsulation of the Internet Protocol designed to work over serial ports and modem connections. It is documented in RFC 1055.

Proxy ARP is a technique by which a device on a given network answers the ARP queries for a network address that is not on that network. The ARP Proxy is aware of the location of the traffic's destination, and offers its own MAC address as (ostensibly final) destination.

Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system (AS). It is defined as OSPF Version 2 in RFC 2328 (1998) for IPv4.

Kerberos is a secure method for authenticating a request for a service in a computer network. Kerberos was developed in the Athena Project at the Massachusetts Institute of Technology (MIT). The name is taken from Greek mythology; Kerberos was a three-headed dog who guarded the gates of Hades.

A multihomed host is physically connected to multiple data links that can be on the same or different networks. For example, a computer with a Windows NT 4.0 Server and multiple IP addresses can be referred to as "multihomed" and may serve as an IP router.

The Network Virtual Terminal (NVT) is a representation of a basicterminal and provides a standard that the computers on either end of a Telnet connection are assumed to follow. It defines how data and commands are sent across the network.

The Gateway-to-Gateway Protocol (GGP) is an obsolete protocoldefined for routing datagrams between Internet gateways. TheGateway-to-Gateway Protocol was designed as an Internet Protocol(IP) datagram service similar to the Transmission Control Protocol(TCP) and the User Datagram Protocol (UDP).

Border Gateway Protocol (BGP) is a standardized exterior gateway protocoldesigned to exchange routing and reachability information among autonomous systems (AS) on the Internet. The protocol is often classified as a path vector protocol but is sometimes also classed as a distance-vector routing protocol.

Within the Internet, an autonomous system (AS) is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators on behalf of a single administrative entity or domain that presents a common, clearly defined routing policy to the Internet.

Exterior Gateway Protocol (EGP) is a protocol for exchanging routing information between two neighbor gateway hosts (each with its own router) in a network of autonomous systems. EGP is commonly used between hosts on the Internet to exchange routing table information.

The mail gateway is a machine that handles connections between networks that run different communications protocols or communications between different networks that use the same protocol.

The Wide Mouth Frog protocol is a computer network  authentication protocol designed for use on insecure  networks (the Internet for example). It allows individuals  communicating over a network to prove their identity to  each other while also preventing eavesdropping or replay  attacks, and provides for detection of modification and the  prevention of unauthorized reading 

The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing,and, and ion.

Silly window syndrome is a problem in computer networking caused by poorly implemented TCP flow control. A serious problem can arise in the sliding window operation when the sending application program creates data slowly, the receiving application program consumes data slowly, or both.

A network region is a group of IP endpoints that share common characteristics and resources. Every IP endpoint on an Avaya Communication Manager system belongs to anetwork region

Multicast IP Routing protocols are used to distribute data (for example, audio/video streaming broadcasts) to multiple recipients. Usingmulticast, a source can send a single copy of data to a single multicastaddress, which is then distributed to an entire group of recipients.

Traffic shaping, also known as packet shaping, Quality of Service (QoS) or bandwidth management, is the manipulation and prioritization of network traffic to reduce the impact of heavy users or machines from effecting other users.

Packet filtering is a firewall technique used to control network access by monitoring outgoing and incoming packets and allowing them to pass or halt based on the source and destination Internet Protocol (IP) addresses, protocols and ports.

The bandwidth of the transmission path is logically divided into separate virtual paths and identified using the VPI in the ATM header. Each virtual path is allocated a fixed amount of bandwidth. Virtual paths do not dynamically vary their bandwidths beyond what has been allocated.

The bandwidth of a virtual path is logically divided into separate virtual channels using a virtual channel identifier in the ATM header. Unlike virtual paths, virtual channels share the bandwidth within a virtual path dynamically.

Logical Link Control (LLC) is the higher of the two data link layer sublayers defined by the IEEE. The LLC sublayer handles error control, flow control, framing, and MAC-sublayer addressing. The most prevalent LLC protocol is IEEE 802.2, which includes both connectionless and connection-oriented variants.

It provides a framework for discussing network operations and design.

OSI reference model inspires the various protocol stacks physically implemented.e.g. TCP/IP ,X.25.

So it lays down the basic framework design for communication

Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router

UNIX is a computer Operating System which is capable of handling activities from multiple users at the same time. Unix was originated around in 1969 at AT&T Bell Labs by Ken Thompson and Dennis Ritchie. This tutorial gives a very good understanding on Unix.

Modern computing environments tend to favor form over function: the primary objective in their design is ease of use for non-experts.

Unix is a naked celebration of function over form. The premium is on control, efficiency and flexibility. Its audience is the power user.

The origin of Unix's power is an organic design philosophy that emphasizes linguistic abstraction and composition.

In Unix, a word is worth a thousand mouse clicks.

Unix is a family of operating systems and environments that exploits the power of linguistic abstraction and composition to orchestrate tasks.

Unix users spend a lot of time at the command line.

Unix (officially UNIX) is a registered trademark of The Open Group that refers to a family of computer operating systems and tools conforming to The Open Group Base Specification, Issue 7 (also known as POSIX.1-2008 or IEEE Std 1003.1 - 2008). To use the Unix trademark, an operating system vendor must pay a licensing fee and annual trademark royalties to The Open Group. Officially licensed Unix operating systems (and their vendors) include OS X (Apple), Solaris (Oracle), AIX (IBM), IRIX (SGI), and HP-UX (Hewlett-Packard).

Note:Operating systems that behave like Unix systems and provide similar utilities, but do not conform to Unix specification or are not licensed by The Open Group, are commonly known as Unix-like systems. These include a wide variety of Linux distributions (e.g., Red Hat Enterprise Linux, Ubuntu, and CentOS) and several descendants of the Berkeley Software Distribution operating system (e.g., FreeBSD, OpenBSD, and NetBSD).

Proprietary Unix operating systems (and Unix-like variants) run on a wide variety of digital architectures, and are commonly used on web servers, mainframes, and supercomputers. In recent years, smartphones, tablets, and personal computers running versions or variants of Unix have become increasingly popular.

The original Unix operating system was developed at AT&T's Bell Labs research center in 1969. In the 1970s and 1980s, AT&T licensed Unix to third-party vendors, leading to the development of several Unix variants, including Berkeley Unix, HP-UX, AIX, and Microsoft's Xenix. In 1993, AT&T sold the rights to the Unix operating system to Novell, Inc., which a few years later sold the Unix trademark to the consortium that eventually became The Open Group.

Unix was developed using a high-level programming language (C) instead of platform-specific assembly language, enabling its portability across multiple computer platforms. Unix also was developed as a self-contained software system, comprising the operating system, development environment, utilities, documentation, and modifiable source code. These key factors led to widespread use and further development in commercial settings, and helped Unix and its variants become an important teaching and learning tool used in academic settings.

The last field, called either command or login command, is used to specify what shell the user will use when he logs in.

 User rights:user rights is that user is authorized to used password.if his password/file/dir is expired he is not able to login. As an Administrator you can determine wich user has the right to access those devices. 

 User permission:permission is user is permitted to to use file/directory. thatis authentication if he is authentication for particular file or not. Permissions are assigned to objects like file or directory while rights are assigned to user.

If you're using BASH, just press CTRL+Z, which will suspend the process, and then use the "bg" command to send it to the background.

The fdisk partitioning tool is available in all distributions.

•  CRON is for running task at a regular base (every hour, day, first of the month etc), cron job is used to schedule the job. It is used for maintain the daily routing work.
• AT on the other hand, is a one-shot. At a certain time (tomorrow at 14:00) a job is started. Once. At schedule the task at only once 

The dmesg command displays the system messages contained in the kernel ring buffer. By using this command immediately after booting your computer, you will see the boot messages. 

dmesg keeps track of all log messages generated by the system. The boot messages can be viewed using following command: cat /var/log/messages

The operating system is the most important program that runs on acomputer. Every general-purpose computer must have an operating system to run other programs and applications. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files anddirectories on the disk, and controlling peripheral devices such asdisk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system

When the page (data) requested by a program is not available in the memory, it is called as a page fault. This usually results in the application being shut down.

A page is a fixed length memory block used as a transferring unit between physical memory and an external storage. A page fault occurs when a program accesses a page that has been mapped in address space, but has not been loaded in the physical memory.

With a threads package, a programmer can create multiple threads within a process. Threads execute concurrently and, within a multithreaded process, there are at any time multiple points of execution. Threads execute within a single address space. Multithreaded programming offers the following advantages:

• · Performance

Threads improve the performance (throughput, computational speed, responsiveness, or some combination of these) of a program. Multiple threads are useful in a multiprocessor system where threads run concurrently on separate processors. In addition, multiple threads also improve program performance on single processor systems by permitting the overlap of input and output or other slow operations with computational operations.

You can think of threads as executing simultaneously, regardless of the number of processors present. You cannot make any assumptions about the start or finish times of threads or the sequence in which they execute, unless explicitly synchronized.

• · Shared Resources

An advantage of using multiple threads over using separate processes is that the former share a single address space, all open files, and other resources.

• · Potential Simplicity

Multiple threads can reduce the complexity of some applications that are inherently suited for threads.

Disadvantages of using threads include: 1)Global variables are shared between threads.Inadvertent modification of shared variables can be disastrous. 2)Many library functions are not thread safe. 3)If one thread crashes the whole application crashes. 4)Memory crash in one thread kills other threads sharing the same memory, unlike processes. 5)There is a lack of coordination between threads and operating system kernel. Therefore, process as whole gets one time slice irrespective of whether process has one thread or 1000 threads within. It is up to each thread to relinquish control to other threads. 6)User-level threads requires non-blocking systems call i.e., a multi threaded kernel. Otherwise, entire process will blocked in the kernel, even if there are runnable threads left in the processes. For example, if one thread causes a page fault, the process blocks. 7)Threads are totally dependent on Operating Systems.  8)Threads if executed serially may increase the time complexity.

A compiler is a special program that processes statements written in a particular programming language and turns them into machine language or "code" that a computer's processor uses.

A compiler works with what are sometimes called 3GL and higher-level languages.

Thus a compiler is a software program that transforms high-level source code that is written by a developer in a high-level programming language into a low level object code (binary code) in machine language, which can be understood by the processor. The process of converting high-level programming into machine language is known as compilation.

The processor executes object code, which indicates when binary high and low signals are required in the arithmetic logic unit of the processor.

A library is a collection of precompiled routines that a program can use. The routines, sometimes called modules, are stored in object format. Libraries are particularly useful for storing frequently used routines because you do not need to explicitly link them to every program that uses them.

The page stealer and the fault handler thrash because of the shortage of the memory. If the sum of the working sets of all processes is greater that the physical memory then the fault handler will usually sleep because it cannot allocate pages for a process. This results in the reduction of the system throughput because Kernel spends too much time in overhead, rearranging the memory in the frantic pace.

Kernel follows Round Robin scheme choosing a swap device among the multiple swap devices in Unix System V.

A kernel is the core component of an operating system. Using interprocess communication and system calls, it acts as a bridge between applications and the data processing performed at the hardware level. When an operating system is loaded into memory, the kernel loads first and remains in memory until the operating system is shut down again. The kernel is responsible for low-level tasks such as disk management, task management and memory management.

The kernel is responsible for:

• Process management for application execution
• Memory management, allocation and I/O
• Device management through the use of device drivers
• System call control, which is essential for the execution of kernel services

There are five types of kernels:

Monolithic Kernels: All operating system services run along the main kernel thread in a monolithic kernel, which also resides in the same memory area, thereby providing powerful and rich hardware access. Microkernels: Define a simple abstraction over hardware that use primitives or system calls to implement minimum OS services such as multitasking, memory management and interprocess communication. Hybrid Kernels: Run a few services in the kernel space to reduce the performance overhead of traditional microkernels where the kernel code is still run as a server in the user space. Nano Kernels: Simplify the memory requirement by delegating services, including the basic ones like interrupt controllers or timers to device drivers. Exo Kernels: Allocate physical hardware resources such as processor time and disk block to other programs, which can link to library operating systems that use the kernel to simulate operating system abstractions.

In the Monolithic(Macro) Kernal entire kernel functionalty is  organised into single block.LINUX is a example of  Monolithic Kernel. In the Micro Kernel the functionality of kernel is minimal. i.e one with process management,file management,etc... Some RTOS( I think MU COS)is example for this. 

Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures.

A link is a pointer or reference to another file. A directory in UNIX has a list of file names and their corresponding inodes. A directory entry can have an Inode pointing to another file. This is a hard link. When a hard link is made, then the i-numbers of two different directory file entries point to the same inode. A symbolic link or a soft link is a special type of file containing links or references to another file or directory in the form of a path. The path may be relative or absolute. To create a symbolic link, following command is used:  

Ln –s target link_name

Here, target is the path and link_name is the name of the link. Symbolic links can be created to create a file system based on different views of the user.

Link is a utility program in UNIX which establishes a hard link from one directory to another directory. A hard link is a reference to a directory or to file on storage media. A symbolic link is a type of file. It contains references to another file directory in the form of absolute or a relative path.

• A Unix pipe provides a one-way flow of data.
• A pipe can be explicitly created in Unix using the pipe system call. Two file descriptors are returned--fildes[0] and fildes[1], and they are both open for reading and writing. A read from fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis and a read from fildes[1] accesses the data written to fildes[0] also on a FIFO basis. 
• When a pipe is used in a Unix command line, the first process is assumed to be writing to stdout and the second is assumed to be reading from stdin. So, it is common practice to assign the pipe write device descriptor to stdout in the first process and assign the pipe read device descriptor to stdin in the second process. This is elaborated below in the discussion of multiple command pipelines.

The “inode” data structure is used to maintain the file identification. Each file has a separate inode and a unique inode number.

cat command is used to display the contents on to the screen

$cat filename

more command is used to diaplay a file with pausing.

$more filename

• Job control

The ability to stop jobs with CTRL-Z and move them to the foreground or background with the fg and bg commands.

• Aliases

The ability to define shorthand names for commands or command lines.

• Functions

The ability to store your own shell code in memory instead of files. Functions increase programmability and efficiency. (Functions have been common in the Bourne shell for many years.)

• Command history

The ability to recall previously entered commands.

The Korn shell’s major new features include:

• Command-line editing

This feature allows you to use vi or Emacs-style editing commands on your command lines.

• Integrated programming features

The functionality of several external Unix commands, includingtest, expr, getopt, and echo, has been integrated into the shell itself, enabling common programming tasks to be done more cleanly and without creating extra processes.

• Control structures

Additional flow-control structures, especially the select construct, enable easy menu generation.

• Debugging primitives

These features make it possible to write tools that help programmers debug their shell code.

• Regular expressions

Well known to users of Unix utilities like grep and awk, regular expressions (albeit with a different syntax) have been added to the standard set of filename wildcards and to the shell variable facility.

• Advanced I/O features

Several new facilities for control of process I/O, including the ability to do two-way communication with concurrent processes (coroutines), and to connect to network services.

• New options and variables

These options and variables give you more ways to customize your environment than the standard Unix shells do.

• Increased speed

The Korn shell often executes the same shell program considerably faster than the Bourne shell does.

• Security features

Features designed to help protect against “Trojan horses” and other types of break-in schemes.

Major new features in the 1993 version include:

• POSIX compliance

Compliance with POSIX, an international standard for portable shell programming, makes it possible to write and use portable shell scripts.

• Arithmetic for loops

This new control structure lets you program more naturally when looping a fixed number of times.

• Floating-point arithmetic

The ability to use floating-point numbers and new built-in arithmetic functions enrich the shell as a programming language.

• Structured variable names

New syntax for variable names provides facilities similar to C structures and Ada records for grouping related items together in a variable.

• Indirect variable references

This facility eases shell function programming for manipulating global variables.

• Associative arrays

A powerful data-management facility that is similar to those in awkor perl.

• Additional text manipulation facilities

There are even more ways to match patterns and substitute variables.

• More built-in commands
• Additional commands improve efficiency and increase script portability.

• sh – Bourne shell
• csh – C SHell
• bash – Bourne Again Shell
• tcsh – enhanced C Shell
• zsh – Z SHell
• ksh – Korn SHell

A theme is a style applied to an entire Activity or application, rather than an individual View. When a style is applied as a theme, every View in the Activity or application will apply each style property that it supports. For example, you can apply the same CodeFont style as a theme for an Activity and then all text inside that Activity will have green monospace font.

A layout resource defines the architecture for the UI in an Activity or a component of a UI.

FILE LOCATION:

res/layout/filename.xml

The filename will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

Resource pointer to a View (or subclass) resource.

RESOURCE REFERENCE:

In Java: R.layout.filename In XML: @[package:]layout/filename

exit can be used to quit shell script if statement

Installing bash for shell script environment

The Zend Engine is the open source scriptingengine that interprets the PHP programming language. It was originally developed by Andi Gutmans and Zeev Suraski while they were students at the Technion - Israel Institute of Technology. They later founded a company called Zend Technologies in Ramat Gan, Israel.

PAT(Port Address Translation) have one IP address and various host using that IP to connect to the outside world each host with unique source port number which is used to descriminate one host from the pther host

unlink() is a function for file system handling, unlink() is used to delete files. Suppose you have uploaded a file and wants to delete this file through the coding then unlink() function is used to delete the file.

unset() is a function for variable management. It will make a variable undefined. Or we can say that unset() is used to null out the value of a given variable. OR Unset () is used to destroy a variable in PHP. In can be used to remove a single variable, multiple variables, or an element from an array.

Unlink It is used to delete the file used in the context. Example : unlink('test.html'); Unset  It is used to unset or destroy the variable. Example : unset($var);

Process States

As a process executes, it changes state. The state of a process is defined as the current activity of the process.

New The process is being created.

Ready The process is waiting to be assigned to a processor. Ready processes are waiting to have the processor allocated to them by the operating system so that they can run.

Running Process instructions are being executed (i.e. The process that is currently being executed).

Waiting The process is waiting for some event to occur (such as the completion of an I/O operation).

Terminated The process has finished execution.

Process Control Block, PCB

Each process is represented in the operating system by a process control block (PCB) also called a task control block. PCB is the data structure used by the operating system. Operating system groups all information that needs about particular process.

PCB contains many pieces of information associated with a specific process which are described below.

Pointer Pointer points to another process control block. Pointer is used for maintaining the scheduling list.

Process State Process state may be new, ready, running, waiting and so on.

Program Counter Program Counter indicates the address of the next instruction to be executed for this process.

CPU registers CPU registers include general purpose register, stack pointers, index registers and accumulators etc. number of register and type of register totally depends upon the computer architecture.

Memory management information This information may include the value of base and limit registers, the page tables, or the segment tables depending on the memory system used by the operating system.This information is useful for deallocating the memory when the process terminates.

Accounting information This information includes the amount of CPU and real time used, time limits, job or process numbers, account numbers etc.

Base services - It is a part of the standard OS. Extended services - These are add-on modular software components that are layered on top of base service.

(i) Program Execution

(ii) Handling Input/output Operations

(iii) Manipulation of File System

(iv) Error Detection and Handling

(v) Resource Allocation

(vi) Accounting

(vii) Information and Resource Protection

Sparse Indexing 

In sparse index, index records are not created for every search key. An index record here contains a search key and an actual pointer to the data on the disk. To search a record, we first proceed by index record and reach at the actual location of the data. If the data we are looking for is not where we directly reach by following the index, then the system starts sequential search until the desired data is found.

Specialization is the reverse process of Generalization means creating new sub classes from an existing class.

Your superclass is a generalized class , but your subclass will be a specialized inheritor of your superclass. It becomes more specialized and less generalized as you move down the inheritance hierarchy .

Generalization

Generalization is the process of extracting shared characteristics from two or more classes, and combining them into a generalized superclass. Shared characteristics can be attributes, associations, or methods.

Specialization

If some new subclasses are created from an existing superclass to do specific job of the superclass, then it is known as specialization.

The Naive Bayes algorithm is based on conditional probabilities. It uses Bayes' Theorem, a formula that calculates a probability by counting the frequency of values and combinations of values in the historical data.

Bayes' Theorem finds the probability of an event occurring given the probability of another event that has already occurred. If Brepresents the dependent event and A represents the prior event, Bayes' theorem can be stated as follows.

Bayes' Theorem:

Prob(B given A) = Prob(A and B)/Prob(A)

To calculate the probability of B given A, the algorithm counts the number of cases where A and B occur together and divides it by the number of cases where A occurs alone.

Yes, you remove the attribute and then re-save() the object.

Each journal (group) write is consistent and won't be replayed during recovery unless it is complete.

A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope.

There is extra memory mapped file activity with journaling. This will further constrain the limited db size of 32 bit builds. Thus, for now journaling by default is disabled on 32 bit systems. 

MongoDB by default prefers high insert rate over transaction safety. If you need to load tons of data lines with a low business value for each one, MongoDB should fit.

MongoDB is an open-source database developed by MongoDB, Inc. MongoDB stores data in JSON-like documents that can vary in structure. Related information is stored together for fast query access through the MongoDB query language. MongoDB uses dynamic schemas, meaning that you can create records without first defining the structure, such as the fields or the types of their values. You can change the structure of records (which we call documents) simply by adding new fields or deleting existing ones. This data model give you the ability to represent hierarchical relationships, to store arrays, and other more complex structures easily. Documents in a collection need not have an identical set of fields and denormalization of data is common. MongoDB was also designed with high availability and scalability in mind, and includes out-of-the-box replication and auto-sharding.

MySQL and MongoDB are both free and open source databases. MySQL and MongoDB have a lot of basic differences in terms of data representation, querying, relationships, transactions, schema design and definition, normalization, speed and performance. By comparing MySQL with MongoDB, we are comparing Relational and non-relational databases. 

Types of NoSQL Databases

There are four general types of NoSQL databases, each with their own specific attributes:

• Graph database – Based on graph theory, these databases are designed for data whose relations are well represented as a graph and has elements which are interconnected, with an undetermined number of relations between them. Examples include: Neo4j and Titan.
• Key-Value store – we start with this type of database because these are some of the least complex NoSQL options. These databases are designed for storing data in a schema-less way. In a key-value store, all of the data within consists of an indexed key and a value, hence the name. Examples of this type of database include:Cassandra, DyanmoDB, Azure Table Storage (ATS), Riak, BerkeleyDB.
• Column store – (also known as wide-column stores) instead of storing data in rows, these databases are designed for storing data tables as sections of columns of data, rather than as rows of data. While this simple description sounds like the inverse of a standard database, wide-column stores offer very high performance and a highly scalable architecture. Examples include: HBase, BigTable and HyperTable.
• Document database – expands on the basic idea of key-value stores where “documents” contain more complex in that they contain data and each document is assigned a unique key, which is used to retrieve the document. These are designed for storing, retrieving, and managing document-oriented information, also known as semi-structured data. Examples include: MongoDB and CouchDB.

Derived from the word humongous, MongoDB is a scalable and high-performance open source database designed to handle document-oriented storage. MongoDB was written in C++ and features replication & High Availability, mirror across LANs and WANs for scale, auto-sharing, rich querying and more.

The scope of a static variable is local to the block in which the variable is defined. However, the value of the static variable persists between two function calls

Arrays can't be passed by values. Because , the array name is evaluated to be a pointer to the first element of the array. e.g. when we pass array x, its equivalent to &x[0] i.e. pointer to the first element. Its type is, therefore, int *, and a called function uses this pointer (passed as an argument) to indirectly access the elements of the array. e.g . int main() { void function1(int A[],int n); int x[10],i; for(i=0;i<10;i++) { x[i] = 10; } function1(x,10); }  void function1(int A[],int n)  { ..../* some processing on the array */  } In the above example,prototype shows the first formal parameter as an integer array without specifying the size. In C, this syntax is interpreted as a pointer variable; so array A is declared as an int * variable.  This is the unique feature of C is that array access is always indirect; thus making it particularly easy for a called function to indirectly access elements of an array and store or retrieve values.  

Critical task completion on time is guaranteed by a hard real time system. The tasks needed for delays in the system are to be bounded by retrieving the stored data at the time which takes the operating system to complete any request. A critical task obtains a priority over other tasks and maintaining that priority until the completion of the task. This is performed by a soft real time system. The system kernel delays need to be bounded as in the case of hard real time system.

By the Template Class

A few differences in features are: 1.The psos priority is reverse of vxworks. 2.psos supports posix 1003.1 while vxworks it is 1003.1b. 3.In psos device driver architecture is different than vxworks. 4.Also vxworks has interrupt latency<4.33 microsecs while psos its higher. Other then these both work in same manner and follow same architecture. Also as psos is getting killed no fresh development work is supported by windriver for psos. Also vxworks development environment is much more user friendly then psosenvironment becos vxworks IDE mimics mostly visual studio.

Arrays can't be passed by values. Because , the array name is evaluated to be a pointer to the first element of the array. e.g. when we pass array x, its equivalent to &x[0] i.e. pointer to the first element. Its type is, therefore, int *, and a called function uses this pointer (passed as an argument) to indirectly access the elements of the array.

Object oriented language

Object-oriented language supports all the features of OOPs.

Object-oriented language doesn't has in-built object.

Object-oriented languages are C++, C#, Java etc.

Object based language

Object-based language doesn't support all the features of OOPs like Polymorphism and Inheritance

Object-based language has in-built object like javascript has window object.

Object-based languages are Javascript, VB etc.

Single Inheritance

Multiple Inheritance

Hierarchical Inheritance

Multilevel Inheritance

Interrupt latency is the responce time of interrupt that meeans the time taken by the device to recieve it and then acknowledge after that it will transfer to particular ISR.

Computer architecture is a specification detailing how a set of software and hardware technology standards interact to form a computer system or platform. In short, computer architecture refers to how a computer system is designed and what technologies it is compatible with.

As with other contexts and meanings of the word architecture, computer architecture is likened to the art of determining the needs of the user/system/technology, and creating a logical design and standards based on those requirements.

A very good example of computer architecture is Von Neumann architecture, which is still used by most types of computers today. This was proposed by the mathematician John Von Neumann in 1945. It describes the design of an electronic computer with its CPU, which includes the arithmetic logic unit, control unit, registers, memory for data and instructions, an input/output interface and external storage functions. There are three categories of computer architecture:  

• System Design: This includes all hardware components in the system, including data processors aside from the CPU, such as the graphics processing unit and direct memory access. It also includes memory controllers, data paths and miscellaneous things like multiprocessing and virtualization
• Instruction Set Architecture (ISA): This is the embedded programming language of the central processing unit. It defines the CPU's functions and capabilities based on what programming it can perform or process. This includes the word size, processor register types, memory addressing modes, data formats and the instruction set that programmers use.
• Microarchitecture: Otherwise known as computer organization, this type of architecture defines the data paths, data processing and storage elements, as well as how they should be implemented in the ISA.

Different qualifiers in C

1) Volatile: A variable should be declared volatile whenever its value could change unexpectedly. In practice, only three types of variables could change:  ? Memory-mapped peripheral registers  ? Global variables modified by an interrupt service routine  ? Global variables within a multi-threaded application  2) Constant: The addition of a 'const' qualifier indicates that the (relevant part of the) program may not modify the variable.

Advantage:  Macros and Inline functions are efficient than calling a normal function. The times spend in calling the function is saved in case of macros and inline functions as these are included directly into the code. Macro is expanded by preprocessor and inline function are expanded by compiler. More over inline functions are used to overcome the overhead of function calls. Macros are used to maintain the readbility and easy maintainence of the code. Disadvantage:  Macros and inline functions increased the size of executable code.   Expressions passed as arguments to inline functions are evaluated only once while _expression passed as argument to inline functions are evaluated more than once.   

Along with the life time of a variable, storage class also determines variable'sstorage location (memory or registers), the scope (visibility level) of the variable, and the initial value of the variable. There are four storage classes in C those are automatic, register, static, and external.

It is scheduled by an OS. In general, it is contained in a process. So, multiple threads can exist within the same process. It shares the resources with the process: The memory, code (instructions), and global variable (context - the values that its variables reference at any given moment). On a single processor, each thread has its turn by multiplexing based on time. On a multiple processor, each thread is running at the same time with each processor/core running a particular thread.

ASP.NET is a unified Web development model that includes the services necessary for you to build enterprise-class Web applications with a minimum of coding. ASP.NET is part of the .NET Framework, and when coding ASP.NET applications you have access to classes in the .NET Framework. You can code your applications in any language compatible with the common language runtime (CLR), including Microsoft Visual Basic and C#. These languages enable you to develop ASP.NET applications that benefit from the common language runtime, type safety, inheritance, and so on.

In short ASP.NET, the next generation version of Microsoft’s ASP, is a programming framework used to create enterprise-class web sites, web applications, and technologies. ASP.NET developed applications are accessible on a global basis leading to efficient information management. Whether you are building a small business web site or a large corporate web application distributed across multiple networks, ASP.NET will provide you all the features you could possibly need…and at an affordable cost: FREE!

The Enterprise version of Java, also called Advanced Java, has a much larger usage of Java, like development of web services, networking, server side scripting and other various web based applications. J2EE is a community driven edition, i.e. there is a lot of continuous contributions from industry experts, Java developers and other open source organisations. J2EE uses many components of J2SE, as well as, has many new features of it’s own like Servlets, JavaBeans, Java Message Services, adding a whole new functionalities to the language. J2EE uses HTML, CSS, JavaScript etc., so as to create web pages and web services. It’s also one of the most widely accepted web development standard.

Web design is the planning and creation of websites. This includes the information architecture, user interface, site structure, navigation, layout, colors, fonts and imagery. All of these are combined with the principles of design to create a website that meets the goals of the owner and designer.

Java vs Python

It depends what you aspire to achieve. Both differs in methods again similar in applications. If you have prior knowledge of programming like C, C++ then Java would get a bit easier to grasp on the otther hand python yields compact code with relatively less complexity in syntaxes and expressions for beginners. Both are equally good in their objectives therefore your choice depends on your goal.

Considering Excel you may use predefined arithmatic summation function'=SUM(parameter1,parameter2)' in your case it is =SUM(Cell numbers rowcolumn are parameters comma seperated) or =SUM(20,40)..Without using predefined function you can use '=20+30' on a specific cell..Now there is one more rare possible operation called string concatenation which would yield 2040 but it doesn't as your values were not in quotes "20"+"40". Thank you

Correction: "20"+"30"..2030...always remember to use an equal to '=' also known as initializing operator, prefixed before your expression.

Your output is 50

Chemical formula: C4H4O4

Also known as: Hydroxybutanedioic acid, 2-Hydroxysuccinic acid, L-Malic acid, D-Malic acid 

Maleic Acid is Strongly Acidic

• At concentration of 1 mM, it has a pH of 3.33
• At concentration of 10 mM, it has a pH of 2.74 
• At concentration of 100 mM, it has a pH of 2.21 

Molar mass116.07 g·mol−1

Melting point135 °C (275 °F; 408 K) (decomposes)

Appearance:White solidDensity1.59 g/cm³

Maleic Acid contains not less than 99.0 percent and not more than 101.0 percent of C4H4O4, calculated on the anhydrous basis.

Application Programming Interface

Ans: 103  ...explanation as per assumption

As far your equation:x*y=x*x+y*y-x*y......9*11

Let us assume, 

x * y = 9 * 11    !!although 9*11=99 just kidding :-)!!

So,

x=9, y=11

x^2 = 9^2 = 81

y ^ 2 = 11 ^ 2 = 121

now substitute the equation:

as assumed  x=9 and y=11

(9*9)+(11*11)-(9*11) following BODMAS rule

81 + 121 - 99 = 202 - 99 = 103 is your answer.

Thank You

D) sequential entry one by one

C) 3

Applying the postfix expression evaluation.

Following is algorithm for evaluation postfix expressions. 1) Create a stack to store operands (or values). 2) Scan the given expression and do following for every scanned element.

       a) If the element is a number, push it into the stack

       b) If the element is a operator, pop operands for the operator from stack. Evaluate the operator and push the result                 back to the stack

3) When the expression is ended, the number in the stack is the final answer

Let the given expression be “2 3 1 * + 9 -“. We scan all elements one by one. 1) Scan ‘2’, it’s a number, so push it to stack. Stack contains ‘2’ 2) Scan ‘3’, again a number, push it to stack, stack now contains ‘2 3’ (from bottom to top) 3) Scan ‘1’, again a number, push it to stack, stack now contains ‘2 3 1’ 4) Scan ‘*’, it’s an operator, pop two operands from stack, apply the * operator on operands, we get 3*1 which results in 3. We push the result ‘3’ to stack. Stack now becomes ‘2 3’. 5) Scan ‘+’, it’s an operator, pop two operands from stack, apply the + operator on operands, we get 3 + 2 which results in 5. We push the result ‘5’ to stack. Stack now becomes ‘5’. 6) Scan ‘9’, it’s a number, we push it to the stack. Stack now becomes ‘5 9’. 7) Scan ‘-‘, it’s an operator, pop two operands from stack, apply the – operator on operands, we get 5 – 9 which results in -4. We push the result ‘-4’ to stack. Stack now becomes ‘-4’. 8) There are no more elements to scan, we return the top element from stack (which is the only element left in stack)

Thnak You

A) 1