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 spite of the common usage, none of these systems were simply named "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. 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.

The most common version of DOS this term is used to refer is the Microsoft version, which preceded the Windows operating system and while not in use on modern systems today, 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.