MS-DOS is the operating system created by Microsoft for the first IBM personal computer in 1981. MS-DOS stands for Microsoft Disk Operating System. Learn more reading the full article.

What is MS-DOS?

Stands for Microsoft Disk Operating System, the venerable operating system created by Microsoft for the first IBM personal computer in 1981. MS-DOS evolved through a number of versions until its final release in 1994 as MS-DOS 6.22. The following table highlights the evolution of MS-DOS over the years.

Graphic M-17. Example of running an MS-DOS command.

Versions of MS-DOS

Version Release Date Features
August 1981
Designed for the IBM PC, the initial version was distributed on a single 160-KB floppy disk and ran in 8 KB of RAM.
May 1982
Support was added for double-sided 320-KB disks.
March 1983
Designed for the IBM PC/XT, this version added support for hard disks, hierarchical directories, background printing, and third-party device drivers.
October 1983
Designed for the short-lived IBM PCjr.
August 1984
Designed for the new IBM PC/AT, this version added support for 1.2-MB floppy disks and hard drives larger than 10 MB.
March 1985
Added support for networking and file sharing.
January 1986
Added support for the new 3.5-inch floppy disks.
April 1987
Designed for the IBM PS/2, this version added commands and support for international versions.
February 1988
This version added the mem command, the MS-DOS shell, and support for hard drives larger than 32 MB.
May 1991
For this version, the MS-DOS shell was redesigned, task-swapping was added, and more extensive help, undelete, unformat, and memory-management tools were added.
March 1993
Added the MemMaker utility, real-time disk compression, multiple boot configurations, and antivirus and backup utilities.
October 1993
Added Scandisk for low-level disk checking.
February 1994
Added DriveSpace disk compression.

How It Works

MS-DOS is a 16-bit operating system that runs a command-line interface. MS-DOS commands come in two types:

  • Built-in commands:
    Embedded in the MS-DOS command interpreter Examples include dir, copy, and date.


  • External commands:
    MS-DOS utilities that reside as separate files. Examples include doskey, edit, and smartdrv.


The core operating system consists of three primary files in the root of the system partition:

  • io.sys:
    Controls the boot process and contains basic I/O drivers.


  • msdos.sys:
    Operating system kernel. Applications request operating system services through msdos.sys, which translates them into actions that can be performed by io.sys and device drivers.


    Command interpreter, which provides a user interface for executing MS-DOS commands.


In addition, two text files help control the boot process:

  • config.sys:
    Contains commands that configure hardware components such as memory, keyboard, mouse, and printer


  • autoexec.bat:
    Contains startup commands that configure your prompt and path and run memory-resident programs such as doskey and smartdrv


The remaining external MS-DOS commands and utilities are by default found in the directory C:\DOS.


MS-DOS was so popular in the PC market that other vendors produced their own versions, including IBM’s PC-DOS and Novell’s DR-DOS.

You can add networking functionality to MS-DOS by using the Microsoft Network Client 3.0 for MS-DOS add-on. You can create installation disks for this software using the Network Client Administrator tool in Microsoft Windows NT.