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Unix (/ˈjuː.nɪks/; trademarked as UNIX) is a family of multitasking, multiuser computer operating systemsthat derive from the original AT&T Unix, developed in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others.

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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.

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The UNIX brand has traditionally been applied to the family of multitasking, multiuser computer operating systems that derive from the original AT&T UNIX operating system, developed in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others 

By the most simple definition, UNIX is a computer operating system - the base software that controls a computer system and its peripherals. In this sense, UNIX behaves in the same way that the perhaps more familiar PC operating systems Windows or MacOS behave. 

It provides the base mechanisms for booting a computer, logging in, running applications, storing and retrieving files, etc.

Answer

By the most simple definition, UNIX is a computer operating system - the base software that controls a computer system and its peripherals. In this sense, UNIX behaves in the same way that the perhaps more familiar PC operating systems Windows or MacOS behave. It provides the base mechanisms for booting a computer, logging in, running applications, storing and retrieving files, etc.

More specificially, the word "UNIX" refers to a family of operating systems that are related to one or both of the original UNIX operating systems - BSD and SystemV. Examples of modern UNIX operating systems include IRIX(from SGI), Solaris (from Sun), Tru64 (from Compaq) and Linux (from the Free Software community). Even though these different "flavors" of UNIX have unique characteristics and come from different sources, they all work alike in a number of fundamental ways. If you gain familiarity with any one of these UNIX-based operating systems, you will also have gained at least some familiarity with nearly every other variant of UNIX.

Answer

Intro:

UNIX is an operating system which was first developed in the 1960s, and has been under constant development ever since. By operating system, we mean the suite of programs which make the computer work. It is a stable, multi-user, multi-tasking system for servers, desktops and laptops.

Types of UNIX

There are many different versions of UNIX, although they share common similarities. The most popular varieties of UNIX are:-

Sun Solaris&

GNU/Linux and

MacOS X.

Programming construction:-

The UNIX operating system is made up of three parts; the kernel, the shell and the programs.

1) The kernel

The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.

As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile (which has the effect of removing the filemyfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.

2) The shell

The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).

The adept user can customise his/her own shell, and users can use different shells on the same machine. Staff and students in the school have the tcsh shell by default.

The tcsh shell has certain features to help the user inputting commands.

Filename Completion - By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.

History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.

Files and processes

Everything in UNIX is either a file or a process.

A process is an executing program identified by a unique PID (process identifier).

A file is a collection of data. They are created by users using text editors, running compilers etc.

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Examples of files:

• a document (report, essay etc.)
• the text of a program written in some high-level programming language
• instructions comprehensible directly to the machine and incomprehensible to a casual user, for example, a collection of binary digits (an executable or binary file);
• a directory, containing information about its contents, which may be a mixture of other directories (subdirectories) and ordinary files.

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