DOS (/dɒs/, /dɔːs/) is a platform-independent acronym for Disk Operating System which later became a common shorthand for disk-based operating systems on IBM PC compatibles. DOS primarily consists of Microsoft's MS-DOS and a rebranded IBM version under the name PC DOS, both of which were introduced in 1981. Later compatible systems from other manufacturers are DR DOS (1988), ROM-DOS (1989), PTS-DOS (1993), and FreeDOS (1998). MS-DOS dominated the IBM PC compatible market between 1981 and 1995.