Unix is popular operating system, developed by AT&T in 1969, that was very important in the development of the Internet. It is a multi-processing, multi-user, family of operating systems that run on a variety of architechtures. UNIX allows more than one user to access a computer system at the same time. A widely used Open Source Unix-like operating system. Linux was first released by its inventor Linus Torvalds in 1991. There are versions of Linux for almost every available type of computer hardware from desktop machines to IBM mainframes. The inner workings of Linux are open and available for anyone to examine and change as long as they make their changes available to the public. Because of its robustness and availability, Linux has won popularity in the Open Source community as well as among commercial application developers.