UNIX is an operating system which was first developed in the 1960s and has been changing ever since. UNIX has a suite of programs which make the computer work in a very effecient manner. It is a multi-user, stable, multi-tasking system for a number of applications, desktops, laptops and servers. Some UNIX systems also have a graphical user interface (GUI) similar to PC (Windows, Mac, Linux) which gives the user an easy to use environment. However, to effectively use UNIX a number of operations need to be known which are not covered by the graphical program. Many a times no graphical interface might exist say for example in programs like telnet sessions.

There are many different versions of UNIX, which share many common similarities. The most popular versions of UNIX are GNU/Linux, MacOS X and Sun Solaris (Mac and Linux have GUI).