Thursday, January 3, 2013

Unix

Unix is one of the most popular and widely using operating system in the world.In the late 1960s and early 1970s, Ken Thompson, Dennis Ritchie, and the researchers at AT&T Bell Laboratories developed the Unix operating system, incorporating many of the features of the MULTICS (the Multiplexed Information and Computing Service) research project. Originally, Unix was designed as an operating system for researchers.For researchers flexibility became more important than hardware efficiency.They tailored the system for the needs of a research environment, designing it to run on minicomputers. From its inception, Unix was an affordable and efficient multiuser and multitasking operating system.
The Unix system became popular at Bell Labs as more and more researchers started using the system. In 1973, Dennis Ritchie collaborated with Ken Thompson to rewrite theprogramming code for the Unix system in the C programming language. The first versions of Unix were distributed free to the computer science departments of many noted universities. Throughout the 1970s, Bell Labs began issuing official versions of Unix and licensing the systems to different users. The computer science department of the University of California, Berkeley added many new features to the system that later became standard. In 1975 Berkeley released its own version of Unix, known by its distribution arm, Berkeley Software Distribution (BSD). AT&T developed several research versions of Unix, and in 1983 it released the first commercial version, called System 3. This was later followed by System V, which became a supported commercial software product.
In the late 1970s, BSD Unix became the basis of a research project by the Department of Defense’s Advanced Research Projects Agency (DARPA). As a result, in 1983, Berkeley released a powerful version of Unix called BSD release 4.2. This release included sophisticated file management as well as networking features based on Internet network protocols—the same protocols now used for the Internet. BSD release 4.2 was widely distributed and adopted by many vendors, such as Sun Micro systems. In the mid-1980s, two competing standards emerged, one based on the AT&T version of Unix and the other based on the BSD version. AT&T’s Unix System Laboratories developed System V release 4. Several other companies, such as IBM and Hewlett-Packard, established the Open Software Foundation (OSF) to create their own standard version of Unix. Two commercial standard versions of Unix existed then—the OSF version and System V release 4. Solaris,AIX, HP-UX, FreeBSD, NetBSD, OpenBSD, Mac OS X, UnixWare, and IRIX are popular UNIX variants.
UNIX operating system is made up of several major components like kernel, the shell, the file system, and the commands.The kernel is the part of the operating system that interacts directly with the hardware of a computer, through device drivers that are built into the kernel.The UNIX file system provides a logical method for organizing, storing, retrieving, manipulating, and managing information. Files are organized into a hierarchical file system, with files grouped together into directories.The shell reads  commands and interprets them as requests to execute a program or programs.The shell is called a command interpreter and at the same time it is also a programming language too.

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