Acronym for disk operating system. The term DOS can refer to any operating system, but it is most often used as a shorthand for MS-DOS (Microsoft disk operating system). Originally developed by Microsoft for IBM, MS-DOS is the standard operating system for IBM-compatible personal computers.            

The initial versions of DOS were very simple and resembled another operating system called CP/M. Subsequent versions have become increasingly sophisticated as they have incorporated features of minicomputer operating systems. However, DOS is still a 16-bit operating system, does not support multiple users or multitasking, and has a built-in limitation of 1MB of memory. To exceed this limit, you need a special memory system called EMS (Expanded Memory Specification).


For some time, it has been widely acknowledged that DOS is insufficient for modern computer applications. Microsoft Windows helped alleviate some problems, but until Windows 95, it sat on top of DOS and relied on DOS for many services. New operating systems, including Windows 95 and OS/2 Warp, do not rely on DOS to the same extent, although they can execute DOS-based programs. It is expected that as these operating systems gain market share, DOS will eventually disappear. In the meantime, both IBM and Novell are competing with Microsoft with their own versions of DOS, called PC-DOS and Novell DOS, respectively.