DOS

The acronym DOS stands for disk operating system, an operating system component for computers that provides the abstraction of a file system resident on hard disk or floppy disk secondary storage. In some cases, the disk operating system was called DOS, and on the PC compatible platform, an entire family of operating systems was called DOS.

DOS for other computers

Prior to (and to some extent concurrently with) the development of the IBM PC compatible family of microcomputers, several other operating systems for other architectures were already known as DOS, notably:

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• The DOS initial/simple operating system for the IBM System/360 family of mainframe computers (it later became DOS/VSE, and was eventually just called VSE).
• The DOS operating system for DEC PDP-11 minicomputers (this OS and the computers it ran on were nearly obsolete by the time PCs became common, with various descendants and other replacements).
• The DOS operating system for the Apple Computer's Apple II family of computers. This was the primary operating system for this family from 1979 with the introduction of the floppy disk drive until 1983 with the introduction of ProDOS; many people continued using it long after that date. Usually it was called Apple DOS to distinguish it from MS-DOS.
• Commodore DOS, which was used by 8-bit Commodore computers. Unlike most other DOS systems, it was integrated into the disk drives, not loaded into the computer's own memory.
• Atari DOS, which was used by the Atari 8-bit family of computers. The Atari OS only offered low-level disk-access, so an extra layer called DOS was booted off of a floppy that offered higher level functions such as filesystems.