Disk operating system

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A disk operating system (DOS) is a computer operating system that resides on and can use a disk storage device, such as a floppy disk, hard disk drive, or optical disc. A disk operating system provides a file system for organizing, reading, and writing files on the storage disk, and a means for loading and running programs stored on that disk. Strictly speaking, this definition does not include any other functionality, so it does not apply to more complex OSes, such as Microsoft Windows, and is more appropriately used only for older generations of operating systems.

Disk operating systems for mainframes, minicomputers, microprocessors, and home computers are usually loaded from the disks as part of the boot process.


Early computers predate disk drives, floppy disks, or modern flash storage. Early storage devices such as delay lines, core memories, punched cards, punched tape, magnetic tape, and magnetic drums were used instead. Early microcomputers and home computers used paper tape, audio cassette tape (such as Kansas City standard), or no permanent storage at all. Without permanent storage, program and data entry is done at front panel switches directly into memory or through a computer terminal or keyboard, sometimes controlled by a BASIC interpreter in ROM. When power is turned off, any information is lost.

In the early 1960s, as disk drives became larger and more affordable, various mainframe and minicomputer vendors introduced disk operating systems and modified existing operating systems to use disks.

Hard disks and floppy disk drives require software to manage rapid access to block storage of sequential and other data. For most microcomputers, a disk drive of any kind was an optional peripheral. Systems could be used with a tape drive or booted without a storage device at all. The disk operating system component of the operating system was only needed when a disk drive was used.

By the time IBM announced the System/360 mainframes, the concept of a disk operating system was well established. Although IBM did offer Basic Programming Support (BPS/360) and TOS/360 for small systems, they were out of the mainstream and most customers used either DOS/360 or OS/360.

Most home and personal computers of the late 1970s and 1980s used a disk operating system, most often with "DOS" in the name and simply referred to as "DOS" within their respective communities: CBM DOS for Commodore 8-bit systems, Atari DOS for the Atari 8-bit computers, TRS-DOS for the TRS-80, Apple DOS and ProDOS for the Apple II, and MS-DOS for IBM PC compatibles. CP/M is also a disk operating system, despite not having the "DOS" acronym in the name.

A disk operating system is usually loaded from a disk, but there are exceptions, such as Commodore's disk drives for the Commodore 64 and VIC-20 which contain the DOS in ROM. AmigaDOS also mostly resides in ROM, as a part of a Kickstart firmware (a few select versions are also loaded from disk).

OS extensions

Main OSes

Some disk operating systems are the operating systems for the entire computer system.

See also


  1. ^ Dahmke, Mark (1983-07-01). "CP/M Plus: The new disk operating system is faster and more efficient than CP/M". BYTE Magazine. Vol. 8, no. 7. p. 360.
  2. ^ Wilkinson, Bill (1982). Inside Atari DOS. Greensboro, NC: COMPUTE! Books. ISBN 0-942386-02-7. Archived from the original on 2017-10-02.
  3. ^ A Narrative Description of the Burroughs B5500 Disk File Master Control Program (PDF). Burroughs. October 1966. 1023579. {{cite book}}: |work= ignored (help)
  4. ^ "CDC Operating System History" (PDF). CDC.
  5. ^ GE-635 Comprehensive Operating Supervisor (GECOS) (PDF). General Electricn. July 1964. CPB-1002.
  6. ^ IBM System/360 Basic Programming Support and IBM Basic Operating System/360 Programming Systems Summary (PDF). IBM. {{cite book}}: |work= ignored (help)
  7. ^ IBM System/360 Disk and Tape Operating Systems Concepts and Facilities (PDF) (Ninth ed.). IBM. October 1970. GC24-5030-8. {{cite book}}: |work= ignored (help)
  8. ^ IBM Operating System/360 Concepts and Facilities (PDF). IBM. 1965. C28-6535-0. {{cite book}}: |work= ignored (help)
  9. ^ Control Program-67 /Cambridge Monitor System - (CP-67 /CMS) Version .3.1 - Program Number 3600-05.2.005 - System Description Manual (PDF) (Third ed.). IBM. September 1971. GH20-0802-2. Retrieved January 9, 2023. {{cite book}}: |work= ignored (help)
  10. ^ IBM System/360 Time Sharing System - Concepts and Facilities (PDF) (Fourth ed.). IBM. September 1968. C28-2003-3. Retrieved January 9, 2023. {{cite book}}: |work= ignored (help)
  11. ^ "Definitive List of TRS-80 Model II Operating Systems". Archived from the original on 2017-10-02.