MS-DOS (/ˌɛmˌɛsˈdɒs/ em-es-DOSS; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few operating systems attempting to be compatible with MS-DOS, are sometimes referred to as “DOS” (which is also the generic acronym for disk operating system). MS-DOS was the main operating system for IBM PC compatibles during the 1980s, from which point it was gradually superseded by operating systems offering a graphical user interface (GUI), in various generations of the graphical Microsoft Windows operating system.

IBM licensed and re-released it in 1981 as PC DOS 1.0 for use in its PCs. Although MS-DOS and PC DOS were initially developed in parallel by Microsoft and IBM, the two products diverged after twelve years, in 1993, with recognizable differences in compatibility, syntax, and capabilities.

Beginning in 1988 with DR-DOS, several competing products were released for the x86 platform, and MS-DOS went through eight versions, until development ceased in 2000. Initially, MS-DOS was targeted at Intel 8086 processors running on computer hardware using floppy disks to store and access not only the operating system, but application software and user data as well. Progressive version releases delivered support for other mass storage media in ever greater sizes and formats, along with added feature support for newer processors and rapidly evolving computer architectures. Ultimately, it was the key product in Microsoft’s development from a programming language company to a diverse software development firm, providing the company with essential revenue and marketing resources. It was also the underlying basic operating system on which early versions of Windows ran as a GUI.

History[edit]

MS-DOS command prompt

MS-DOS was a renamed form of 86-DOS – owned by Seattle Computer Products, written by Tim Paterson. Development of 86-DOS took only six weeks, as it was basically a clone of Digital Research’s CP/M (for 8080/Z80 processors), ported to run on 8086 processors and with two notable differences compared to CP/M: an improved disk sector buffering logic, and the introduction of FAT12 instead of the CP/M filesystem. This first version was shipped in August 1980. Microsoft, which needed an operating system for the IBM Personal Computer, hired Tim Paterson in May 1981 and bought 86-DOS 1.10 for US$75,000 in July of the same year. Microsoft kept the version number, but renamed it MS-DOS. They also licensed MS-DOS 1.10/1.14 to IBM, which, in August 1981, offered it as PC DOS 1.0 as one of three operating systems for the IBM 5150 or the IBM PC.

Within a year, Microsoft licensed MS-DOS to over 70 other companies. It was designed to be an OS that could run on any 8086-family computer. Each computer would have its own distinct hardware and its own version of MS-DOS, similar to the situation that existed for CP/M, and with MS-DOS emulating the same solution as CP/M to adapt for different hardware platforms. To this end, MS-DOS was designed with a modular structure with internal device drivers (the DOS BIOS), minimally for primary disk drives and the console, integrated with the kernel and loaded by the boot loader, and installable device drivers for other devices loaded and integrated at boot time. The OEM would use a development kit provided by Microsoft to build a version of MS-DOS with their basic I/O drivers and a standard Microsoft kernel, which they would typically supply on disk to end users along with the hardware. Thus, there were many different versions of “MS-DOS” for different hardware, and there is a major distinction between an IBM-compatible (or ISA) machine and an MS-DOS [compatible] machine. Some machines, like the Tandy 2000, were MS-DOS compatible but not IBM-compatible, so they could run software written exclusively for MS-DOS without dependence on the peripheral hardware of the IBM PC architecture.

This design would have worked well for compatibility, if application programs had only used MS-DOS services to perform device I/O, and indeed the same design philosophy is embodied in Windows NT (see Hardware Abstraction Layer). However, in MS-DOS’s early days, the greater speed attainable by programs through direct control of hardware was of particular importance, especially for games, which often pushed the limits of their contemporary hardware. Very soon an IBM-compatible architecture became the goal, and before long all 8086-family computers closely emulated IBM’s hardware, and only a single version of MS-DOS for a fixed hardware platform was needed for the market. This version is the version of MS-DOS that is discussed here, as the dozens of other OEM versions of “MS-DOS” were only relevant to the systems they were designed for, and in any case were very similar in function and capability to some standard version for the IBM PC—often the same-numbered version, but not always, since some OEMs used their own proprietary version numbering schemes (e.g. labeling later releases of MS-DOS 1.x as 2.0 or vice versa)—with a few notable exceptions.

Microsoft omitted multi-user support from MS-DOS because Microsoft’s Unix-based operating system, Xenix, was fully multi-user. The company planned, over time, to improve MS-DOS so it would be almost indistinguishable from single-user Xenix, or XEDOS, which would also run on the Motorola 68000, Zilog Z8000, and the LSI-11; they would be upwardly compatible with Xenix, which Byte in 1983 described as “the multi-user MS-DOS of the future”. Microsoft advertised MS-DOS and Xenix together, listing the shared features of its “single-user OS” and “the multi-user, multi-tasking, UNIX-derived operating system”, and promising easy porting between them. After the breakup of the Bell System, however, AT&T Computer Systems started selling UNIX System V. Believing that it could not compete with AT&T in the Unix market, Microsoft abandoned Xenix, and in 1987 transferred ownership of Xenix to the Santa Cruz Operation (SCO).

On March 25, 2014, Microsoft made the code to SCP MS-DOS 1.25 and a mixture of Altos MS-DOS 2.11 and TeleVideo PC DOS 2.11 available to the public under the Microsoft Research License Agreement, which makes the code source-available, but not open source as defined by Open Source Initiative or Free Software Foundation standards. Microsoft would later re-license the code under the MIT License on September 28, 2018, making these versions free software.

As an April Fool’s Day joke in 2015, Microsoft Mobile launched a Windows Phone application called MS-DOS Mobile which was presented as a new mobile operating system and worked similar to MS-DOS.

Versions[edit]

Microsoft licensed or released versions of MS-DOS under different names like Lifeboat Associates “Software Bus 86” a.k.a. SB-DOS, COMPAQ-DOS, NCR-DOS or Z-DOS before it eventually enforced the MS-DOS name for all versions but the IBM one, which was originally called “IBM Personal Computer DOS”, later shortened to IBM PC DOS. (Competitors released compatible DOS systems such as DR DOS and PTS-DOS that could also run MS-DOS applications.)

In the former Eastern bloc, MS-DOS derivatives named DCP (Disk Control Program [de]) 3.20 and 3.30 (DCP 1700, DCP 3.3) and WDOS existed in the late 1980s. They were produced by the East German electronics manufacturer VEB Robotron.

The following versions of MS-DOS were released to the public:

MS-DOS 1.x[edit]

MS-DOS (Compaq-DOS) version 1.12 (based on MS-DOS 1.25) for Compaq Personal Computer

• Version 1.24 (OEM) – basis for IBM’s Personal Computer DOS 1.1
• Version 1.25 (OEM) – basis for non-IBM OEM versions of MS-DOS, including SCP MS-DOS 1.25

• Compaq-DOS 1.12, a Compaq OEM version of MS-DOS 1.25; Release date: November, 1983
• TI BOOT V. 1.13, a Texas Instruments OEM version of MS-DOS; Release date: August, 1983
• Zenith Z-DOS 1.19, a Zenith OEM version of MS-DOS 1.25
• Zenith Z-DOS/MS-DOS release 1.01, version 1.25, a Zenith OEM version of MS-DOS; Release date: May, 1983

MS-DOS 2.x[edit]

MS-DOS 2.11 boot disk for the Leading Edge Model D in its sleeve

Support for IBM’s XT 10 MB hard disk drives, support up to 16 MB or 32 MB FAT12 formatted hard disk drives depending on the formatting tool shipped by OEMs, user installable device drivers, tree-structure filing system, Unix-like inheritable redirectable file handles, non-multitasking child processes an improved Terminate and Stay Resident (TSR) API, environment variables, device driver support, FOR and GOTO loops in batch files, ANSI.SYS.

• Version 2.0 (OEM), First version to support 5.25-inch, 180 KB and 360 KB floppy disks; Release date: October 1983
• Version 2.02 (OEM, Compaq); Release date: November 1983
• Version 2.05 (OEM, international support); Release date: October 1983
• Version 2.1 (OEM, IBM only)
• Version 2.11 (OEM)
  • Altos MS-DOS 2.11, an Altos OEM version of MS-DOS 2.11 for the ACT-86C
  • ITT Corporation ITT-DOS 2.11 Version 2 (MS-DOS 2.11 for the ITT XTRA Personal Computer); Release date: July 1985
  • Olivetti M19 came with MS-DOS 2.11
  • Tandy 1000 HX has MS-DOS 2.11 in ROM
  • TeleVideo PC DOS 2.11, a TeleVideo OEM version of MS-DOS 2.11
  • Toshiba MS-DOS 2.11 in ROM drive for the model T1000 laptop
• Version 2.13 (OEM, Zenith); Release date: July 1984
• Version 2.2 (OEM, with Hangeul support)
• Version 2.25 (OEM, with Hangeul and Kanji support)
• Version 2.3 (used on the Toshiba Pasopia 16)

• Windows XP

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  Windows XP

  A version of the Windows NT operating system
  Screenshot of Windows XP running the Luna visual style, showing the start menu, taskbar, and My Computer window
  Developer	Microsoft
  Source model	Closed-source Source-available (through Shared Source Initiative)
  Released to manufacturing	August 24, 2001; 21 years ago
  General availability	October 25, 2001; 20 years ago
  Final release	Service Pack 3 (5.1.2600.5512) / April 21, 2008; 14 years ago
  Marketing target	Consumer and Business
  Update method	Windows Update Windows Server Update Services (WSUS) System Center Configuration Manager (SCCM)
  Platforms	IA-32, x86-64, and Itanium
  Kernel type	Hybrid (NT)
  Userland	Windows API NTVDM (IA-32 only) SFU
  License	Proprietary commercial software
  Preceded by	Windows 2000 (1999) Windows Me (2000)
  Succeeded by	Windows Vista (2007)
  Official website	Windows XP (archived at Wayback Machine)
  Support status
  All editions except Windows XP Embedded, Windows XP 64-bit Edition, Windows Embedded for Point of Service, Windows Embedded Standard 2009 and Windows Embedded POSReady 2009: Mainstream support ended on April 14, 2009 Extended support ended on April 8, 2014 Windows XP 64-bit Edition: Unsupported as of June 30, 2005 Windows XP Embedded: Mainstream support ended on January 11, 2011 Extended support ended on January 12, 2016 Windows Embedded for Point of Service: Mainstream support ended on April 12, 2011 Extended support ended on April 12, 2016 Windows Embedded Standard 2009: Mainstream support ended on January 14, 2014 Extended support ended on January 8, 2019 Windows Embedded POS Ready 2009: Mainstream support ended on April 8, 2014 Extended support ended on April 9, 2019

  Part of a series of articles on
  Windows XP
  New features Releases and editions (Pro x64 · Media Center · Fundamentals) Pocket PC 2002 Windows Server 2003 Windows Mobile 2003 Windows Mobile 5.0 Development history Criticism Removed features XP vs. Vista
  v t e

  Windows XP is a major release of Microsoft’s Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Windows 2000 for high-end and business users and Windows Me for home users, available for any devices running Windows NT 4.0, Windows 98, Windows 2000 and Windows Me that meet the new Windows XP system requirements.

  Development of Windows XP began in the late 1990s under the codename “Neptune”, built on the Windows NT kernel explicitly intended for mainstream consumer use. An updated version of Windows 2000 was also initially planned for the business market. However, in January 2000, both projects were scrapped in favor of a single OS codenamed “Whistler”, which would serve as a single platform for both consumer and business markets. As a result, Windows XP is the first consumer edition of Windows not based on the Windows 95 kernel and MS-DOS. Windows XP removed support for PC-98, i486 and SGI Visual Workstation 320 and 540 and will only run on 32-bit x86 CPUs and devices which use BIOS firmware.

  Upon its release, Windows XP received critical acclaim, noting increased performance and stability (especially compared to Windows Me), a more intuitive user interface, improved hardware support, and expanded multimedia capabilities. Windows XP and Windows Server 2003 were succeeded by Windows Vista and Windows Server 2008, released in 2007 and 2008, respectively. Market share of Windows XP fell below 1% by the end of 2021.

  Mainstream support for Windows XP ended on April 14, 2009, and extended support ended on April 8, 2014. After that, the operating system ceased receiving further support. Windows Embedded POSReady 2009, based on Windows XP Professional, received security updates until April 2019. After that, unofficial methods were made available to apply the updates to other editions of Windows XP. Still, Microsoft discouraged this practice, citing incompatibility issues. As of September 2022, 0.39% of Windows PCs run Windows XP (on all continents, the share is below 1%), and 0.1% of all devices across all platforms run Windows XP. Windows XP is still in widespread use in certain countries, such as Armenia, where over 50% of computers use it.

  Development[edit]

  Main article: Development of Windows XP

  In the late 1990s, initial development of what would become Windows XP was focused on two individual products: “Odyssey”, which was reportedly intended to succeed the future Windows 2000 and “Neptune”, which was reportedly a consumer-oriented operating system using the Windows NT architecture, succeeding the MS-DOS-based Windows 98.

  However, the projects proved to be too ambitious. In January 2000, shortly prior to the official release of Windows 2000, technology writer Paul Thurrott reported that Microsoft had shelved both Neptune and Odyssey in favor of a new product codenamed “Whistler”, named after Whistler, British Columbia, as many Microsoft employees skied at the Whistler-Blackcomb ski resort. The goal of Whistler was to unify both the consumer and business-oriented Windows lines under a single, Windows NT platform. Thurrott stated that Neptune had become “a black hole when all the features that were cut from Windows Me were simply re-tagged as Neptune features. And since Neptune and Odyssey would be based on the same code-base anyway, it made sense to combine them into a single project”.

  At PDC on July 13, 2000, Microsoft announced that Whistler would be released during the second half of 2001, and also unveiled the first preview build, 2250, which featured an early implementation of Windows XP’s visual styles system and interface changes to Windows Explorer and the Control Panel.

  Microsoft released the first public beta build of Whistler, build 2296, on October 31, 2000. Subsequent builds gradually introduced features that users of the release version of Windows XP would recognize, such as Internet Explorer 6.0, the Microsoft Product Activation system and the Bliss desktop background.

  Whistler was officially unveiled during a media event on February 5, 2001, under the name Windows XP, where XP stands for “eXPerience”.