Disk operating system

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A disk operating system (abbreviated 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 must provide a file system for organizing, reading, and writing files on the storage disk. Strictly speaking, this definition does not include any other functionality, it doesn't apply to more complex OSes, such as current generations of PC operating systems like the versions of Microsoft Windows in use, and is more appropriately used only for older generations of operating systems.

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


In the early days of computers, there were no disk drives, floppy disks or modern flash storage devices. Early storage devices such as delay lines, core memories, punched cards, punched tape, magnetic tape, and magnetic drums were used instead. And in the early days of microcomputers and home computers, paper tape or audio cassette tape (see Kansas City standard) or nothing were used instead. In the latter case, program and data entry was done at front panel switches directly into memory or through a computer terminal / keyboard, sometimes controlled by a BASIC interpreter in ROM; when power was turned off any information was lost.

In the early 1960s, as disk drives became larger and more affordable, various mainframe and minicomputer vendors began introducing disk operating systems and modifying existing operating systems to exploit disks.

Both 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 family, TRS-DOS for the TRS-80, Apple DOS and ProDOS for the Apple II, and MS-DOS for IBM PC compatibles.

Usually, a disk operating system was loaded from a disk. Among the exceptions were Commodore, whose DOS resided on ROM chips in the disk drives. The Lt. Kernal hard disk subsystem for the Commodore 64 and Commodore 128 models stored its DOS on the disk, as is the case with modern systems, and loaded the DOS into RAM at boot time; AmigaDOS also mostly resided in ROM as a part of a Kickstart firmware, but a few select versions were also loaded from disk; the British BBC Micro's optional Disc Filing System, DFS, offered as a kit with a disk controller chip, a ROM chip, and a handful of logic chips, to be installed inside the computer.

Disk operating systems that were extensions to the OS[edit]

  • Apple DOS was the primary operating system for the Apple II series of computers, from 1979 with the introduction of the floppy disk drive, until 1983 when it was replaced by ProDOS.
  • Commodore DOS was used on 8-bit Commodore computers such as the Commodore 64. Unlike most other DOS systems, it was integrated into the disk drives, not loaded into the computer's own memory.
  • Atari DOS 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 from a floppy and offered higher level functions such as filesystems.[1] Third-party replacements for Atari DOS were also available: DOS XL, SpartaDOS, MyDOS, TurboDOS, Top-DOS.
  • 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) was an optional component for the Acorn 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.
  • Advanced Disc Filing System (ADFS) was a successor to Acorn's DFS.
  • AMSDOS for the Amstrad CPC computers.
  • GDOS and G+DOS, for the +D and DISCiPLE disk interfaces for the ZX Spectrum.

Disk operating systems that were the main OSs[edit]

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

See also[edit]


  1. ^ Wilkinson, Bill (1982). Inside Atari DOS. Greensboro, NC: COMPUTE! Books. ISBN 0-942386-02-7. Archived from the original on 2017-10-02.
  2. ^ A Narrative Description of the Burroughs B5500 Disk File Master Control Program (PDF). Systems Documentation. Burroughs. October 1966. 1023579.
  3. ^ "CDC Operating System History" (PDF). CDC.
  4. ^ GE-635 Comprehensive Operating Supervisor (GECOS) (PDF). General Electricn. July 1964. CPB-1002.
  5. ^ IBM System/360 Basic Programming Support and IBM Basic Operating System/360 Programming Systems Summary (PDF). Systems Reference Library. IBM.
  6. ^ IBM System/360 Disk and Tape Operating Systems Concepts and Facilities (PDF). Systems Reference Library (Ninth ed.). IBM. October 1970. GC24-5030-8.
  7. ^ IBM Operating System/360 Concepts and Facilities (PDF). Systems Reference Library. IBM. 1965. C28-6535-0.
  8. ^ "Definitive List of TRS-80 Model II Operating Systems". Archived from the original on 2017-10-02.


  1. ^ Now Unisys
  2. ^ Later Honeywell and ultimately Groupe Bull