DOS is a family of closely related operating system that dominated the IBM PC compatible market between 1981 and 1995 (or until about 2000, if one includes DOS-based Microsoft Windows versions (Windows 95, Windows 98, and Windows ME). Related systems include MS-DOS, PC-DOS, DR-DOS (and Novell DOS and OpenDOS, which were based off of DR-DOS), FreeDOS, PTS-DOS, ROM-DOS, JM-OS and several others.
All of these operating systems run on machines with the Intel x86 or compatible CPU, mainly the IBM PC and compatibles. Initially, DOS was not restricted to these, and machine-dependent versions of DOS and similar operating systems were produced for many non-IBM-compatible x86-based machines.
DOS is a single-user, single-task operating system with basic kernel functions that are non-reentrant code; once a process is begun, it must be allowed to run until finished before the same process can be used again. The DOS kernel provides various functions for programs, like displaying characters on...
full article at wikipedia
