Operating System

Mastermind in a computer. The operating system is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs.

Every computer has OS
Every desktop computer uses an operating system. The most popular operating systems in use today are:
 * Windows (Windows XP, 7, 8)
 * Mac OS
 * UNIX
 * Linux

Links

 * Operating System - http://www.webopedia.com/TERM/O/operating_system.html