Disk Operating System (specifically) and disk operating system (generically), most often abbreviated as DOS (not to be confused with the DOS family of disk operating systems for the IBM PC compatible platform), refers to an operating system software used in most computers that provides the abstraction and management of secondary storage devices and the information on them (e.g., file systems for organizing files of all sorts). Such software is referred to as a disk operating system when the storage devices it manages are made of rotating platters (such as hard disks or floppy disks).
In the early days of microcomputing, memory space was often limited, so the disk operating system was an extension of the operating system. This component was only loaded if needed. Otherwise, disk-access would be limited to low-level operations such as reading and writing disks at the sector-level.
In some cases, the disk operating system component (or even the operating system) was known as DOS.
Sometimes, a disk operating system can refer to the entire operating system if it is loaded off a disk and supports the abstraction and management of disk devices. Examples include DOS/360 and FreeDOS. On the PC compatible platform, an entire family of operating systems was called DOS.
Examples of disk operating systems that were extensions to the OS
- 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 a floppy that offered higher level functions such as filesystems.
- MSX-DOS, for the MSX computer standard. Initial version, released in 1984, was nothing but MS-DOS 1.0 ported to Z80; but in 1988 it evolved to version 2, offering facilities such as subdirectories, memory management and environment strings. The MSX-DOS kernel resided in ROM (built-in on the disk controller) so basic file access capacity was available even without the command interpreter, by using BASIC extended commands.
- Disc Filing System (DFS) This was an optional component for the BBC Micro, offered as a kit with a disk controller chip, a ROM chip, and a handful of logic chips, to be installed inside the computer. See also Advanced Disc Filing System.
- AMSDOS, for the Amstrad CPC computers.
- GDOS and G+DOS, for the +D and DISCiPLE disk interfaces for the ZX Spectrum.
- TRS-DOS
- QDOS for the Sinclair QL.
Examples of disk operating systems that were the OS itself
- The DOS/360 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).
- DOS for the IBM PC compatible platform
- The best known family of operating systems named "DOS" is that running on IBM PCs type hardware using the Intel CPUs or their compatible cousins from other makers. Any DOS in this family is usually just referred to as DOS. The original was 86-DOS, which would later become Microsoft MS-DOS. It was also licensed to IBM by Microsoft, and marketed by them as PC-DOS. Digital Research produced a compatible variant known as DR-DOS, which was eventually taken over (after a buyout of Digital Research) by Novell, then by Caldera International. This became Novell DOS, then the open source OpenDOS, before being changed back to DR-DOS. There is also a free and open source version named FreeDOS.