DOS

DOS short for Disk Operating System, is an acronym for several closely related operating systems that dominated the PC market between 1981 and 1995, or until about 2000 including the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.

In the context of x86 PCs, "DOS" most commonly refers to Microsoft's MS-DOS, as well as IBM's rebranded distribution titled PC DOS. These are descended from Tim Paterson's 86-DOS, a source-compatible clone of Digital Research's CP/M. Digital Research would later port CP/M to the PC under the name DR-DOS. While not in use on PCs built since late 2001, when Windows XP replaced MS-DOS with NT, modified modern versions of DOS programs survive on most 32-bit operating systems, and it can be emulated with programs like DOSBox on 64-bit systems.

Several unrelated operating systems for other, non-x86 computers also went by names including "DOS". The first was an IBM mainframe operating system in the 1960s, followed by operating systems for 8-bit home microcomputers, such as DOS 3.3 on Apple II and Atari DOS on Atari 800. These are often referred to simply as "DOS" when discussing machines that use them. While providing many of the same operating system functions for their respective computer systems, programs made for one of these operating systems would not run under others.

Not to be confused with Denial Of Service.