Microsoft Disk Operating System [MS-DOS]


(pronounced “em-ess-DOSS”) (n.) A single-user operating system that runs one program at a time and that is limited to working with one megabyte (MB) of memory, 640 kilobytes (KB) of which are usable for an application program. Special hardware permits EMS-compliant software to exceed the 1-MB limit, and some programs that run on top of DOS, such as Microsoft Windows 3.1, allow the user to load multiple applications at once and to switch between them. Features added to MS-DOS 2.0 and to subsequent versions resulted in two or more incompatible versions of many system calls, the instructions that interface an application with the operating system. MS-DOS is used on the Intel 16- and 32-bit microprocessors in IBM-compatible microcomputers.