DOS: Operating system, IBM PC compatible, Microsoft Windows, Windows 95, Windows 98, Windows Me, DOS/ 360 and successors, AmigaDOS, AMSDOS, ANDOS, Apple DOS, Atari DOS

DOS, short for "Disk Operating System",[1] is a shorthand term for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions Windows 95, 98, and ME. Related systems include MS-DOS, PC DOS, DR-DOS, FreeDOS, PTS-DOS, ROM-DOS, JM-OS, and several others. In spite of the common usage, none of these systems were named simply "DOS" (a name given only to an unrelated IBM mainframe operating system in the 1960s). A number of unrelated, non-x86 microcomputer disk operating systems had "DOS" in their name, and are often referred to simply as "DOS" when discussing machines that use them (e.g. AmigaDOS, AMSDOS, ANDOS, Apple DOS, Atari DOS, Commodore DOS, CSI-DOS, ProDOS, and TRS-DOS). While providing many of the same operating system functions for their respective computer systems, programs running under any one of these operating systems would not run under others