UNIX 
UNIX is a time sharing operating system: a program that controls the resources of a computer and allocates among users in addition to controlling the peripheral devices and managing a file system.

Evolution of UNIX
UNIX was developed in 1969 at AT &T bell laboratories. It was developed by designers, who were involved in the development of less popular MULTICS operating system. UNIX is the brainchild of two persons Ken Thompson and Dennis Ritchie. Their first venture was a modest multitasking system to support two users. This operating system supported an efficient file system, a command interpreter and a set of utilities.

Earlier versions of operating system did not support machine compatibility. But UNIX changed the operating system world scenario entirely by breaking through this seemingly difficult demerit by running on different systems. UNIX was not written in assembly language as most operating system were. It was written in C to aid the machine compatibility feature by making it compatible to different hardware platforms.

Versions of UNIX
The AT & T Bell laboratory where the UNIX was primarily developed was not able to commercialize its products due to a judgment imposing ban passed by government. This judgment forces the AT & T Bell laboratories to sell its product to various academics institutions. Later business establishments joined in the development of the UNIX operating systems. As the results of all these efforts different versions have emerged. Theses versions have been discussed briefly in the forth-coming sections.

Berkeley UNIX
Of all the versions of UNIX this deserves a special mention due to its larger contribution to the development of the operating system. Most of the new features in the UNIX operating system were developed at the University of California, Berkeley.
We could almost say they created a UNIX version of their own. This version was named as BSD UNIX where BSD is the acronym for Berkeley software distribution. Berkeley UNIX has a more efficient file system than AT & T original version and is also equipped with better linking facilities.

Other versions
AT & T Bell laboratories embarked on commercialization of its UNIX after the government’s ban on it was removed. Their earlier versions previously known as “editions” were then changed to “systems”. The first to come in the “system” series was system3, which later became system V Release 3.2 followed this version. There are many other versions of UNIX. These include the Microsoft and sun Microsystems versions. Microsoft’s developed its own version of UNIX and named it ‘ZENIX’ which was later sold off to Santa Cruz operation (SCO). The sun Microsystems versions of UNIX is called as ‘SOLARIS’.

LINUX 
Linux was the first non-commercial version of UNIX. LINUX was developed by Linus Torwalds as his final year project while doing under graduation at Helsinki University in Finland. The licensing made the source code public. Linux is strong in networking and internet features. Linux can run on all PENTIUM PC’S apart from Apple’s power pc and sun’s sparc computers.