History of Mac OS: System 6, System 7, Mac OS 8, Mac OS 9, History of Mac OS X, A/UX, Apple DOS, Apple GS/OS, Apple Lisa, Apple ProDOS, Apple SOS, Apple Computer, Inc.v.Microsoft Corporation

On January 24, 1984, Apple Computer Inc. introduced the Macintosh personal computer, with the Macintosh 128K model, which came bundled with the Mac OS operating system, then known as the System Software. The Macintosh is often credited with popularizing the graphical user interface. The Mac OS has been pre-installed on almost every Macintosh computer ever sold. The operating system is also sold separately at Apple retail stores, and online. The original Mac OS was partially based on the Lisa OS, previously released by Apple for the Lisa computer in 1983 and, as part of an agreement allowing Xerox to buy shares in Apple at a favorable rate, it also used concepts from the Xerox PARC Xerox Alto, which Steve Jobs and several other Macintosh team members had previewed.