The four major operating systems are Windows, Mac OS, Unix, and Linux.1. The most popular is Microsoft Windows. Some version of Windows resides on more than 85 percent of the world's desktops, and when considering just business users, the figure is more than 95 percent. The most recent client version of Windows is Windows 8, a major re-write of prior versions.2. Apple Computer, Inc., developed its own operating system for the Macintosh, Mac OS. The current system is Mac OS X Mountain Lion. Macintosh computers are used primarily by graphic artists and workers in the arts community.3. Unix is an operating system that was developed at Bell Labs in the 1970s. It has been the workhorse of the scientific and engineering communities since then. 4. Linux is a version of Unix that was developed by the open source community. This community is a loosely coupled group of programmers who mostly volunteer their time to contribute code to develop and maintain Linux. The open source community owns Linux, and there is no fee to use it. Linux can run on client computers, but is by far most popular as a server OS.