Originally MS-DOS was designed to be an operating system 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 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 only 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 the same-numbered standard version for the IBM PC with a few notable exceptions.

While MS-DOS appeared on PC clones true IBM computers used PC DOS a rebranded form of MS-DOS. Ironically the dependence on IBM-compatible hardware caused major problems for the computer industry when the original design had to be changed. For example the original design could support no more than 640 kilobytes of memory (the 640 kB barrier) because IBM's hardware design reserved the address space above this limit for peripheral devices and ROM. Manufacturers had to develop complicated schemes (EMS and XMS and other minor proprietary ones) to access additional memory. This limitation would not have been a problem if the original idea of interfacing with hardware through MS-DOS had endured. (However MS-DOS was also a real-mode operating system and the Intel x86 architecture only supports up to 1 MB of memory address space in Real Mode even on Pentium 4 and later x86 CPUs so for simple access to megabytes of memory MS-DOS would have had to be rewritten to run in 80286 or 80386 Protected Mode.) Also Microsoft originally described MS-DOS as "an operating system for Intel 8086-based microcomputers" and the 8086 CPU (and its cousin the 8088) itself has only 1 MiB of total memory address space. Versions Main articles: Comparison of x86 DOS operating systems and Timeline of x86 DOS operating systems

Microsoft licensed or released versions of MS-DOS under different names like SB-DOS or Z-DOS4. Competitors released DOS systems such as DR-DOS and PTS-DOS that could also run DOS applications. The following versions of MS-DOS were released to the public:56 MS-DOS 1.x Version 1.12 (OEM) - Compaq release of PC-DOS 1.10 Version 1.25 (OEM) - Microsoft repackaging of PC-DOS 1.10 MS-DOS 2.x - Support for 10 MB Hard Disk Drives and tree-structure filing system Version 2.0 (OEM) Version 2.1 (OEM) Version 2.11 (OEM) Version 2.2 (OEM) Version 2.21 (OEM) MS-DOS 3.x Version 3.0 (OEM) - Support for larger Hard Disk Drives Version 3.1 (OEM) - Support for Microsoft Networks Version 3.2 (OEM) Version 3.21 (OEM) Version 3.25 (OEM) Version 3.3 (OEM) Version 3.3a (OEM) Version 3.3r (OEM) Version 3.31 (OEM) - Compaq 3.31 supports FAT16 and larger drives. Version 3.35 (OEM) MS-DOS 4.x - includes a graphical/mouse interface. Version 4.00 (OEM) Version 4.01 (OEM) - IBM patched Version 4.00 before Microsoft released it. Version 4.01a (OEM) MS-DOS 5.x Version 5.0 (Retail) - includes a full-screen editor. A number of bugs required reissue. Version 5.0a (Retail) - With this release IBM and Microsoft versions diverge. Version 5.0.500 (WinNT) - All Windows NT 32-bit versions ship with files from DOS 5.0 MS-DOS 6.x Version 6.0 (Retail) - Online help through QBASIC. Disk compression and antivirus included. Version 6.2 (Retail) - Microsoft and IBM alternate versions IBM has 6.1 6.3 Version 6.21 (Retail) - Stacker-infringing DBLSPACE removed. Version 6.22 (Retail) - New DRVSPACE compression. MS-DOS 7.x Version 7.0 (Win9595A) - Support for long file names. New editor. Version 7.1 (Win95B-Win98SE) - Support for FAT32 file system MS-DOS 8.0 Version 8.0 (WinME) - Integrated drivers for faster Windows loading. Version 8.0 (WinXP) - DOS boot disks created by XP and later contain files from WinME. The internal DOS is still 5.0

Microsoft DOS was released through the OEM channel until DRI released DR-DOS 5.0 as a retail upgrade. With PC-DOS 5.00.1 the IBM-Microsoft agreement started to end and IBM entered the retail DOS market with IBMDOS 5.00.1 5.02 6.00 and PC-DOS 6.10 6.30 7.00 and 2000. A number of beta versions have surfaced on the Internet such as 5.0 (a ten-diskette version in the same vein as 4.0) 7.00 beta 1 (based on 6.00) 7.00 beta 2 (based on 6.22). An OEM source package for 6.00 and a late release of 6.2(b) have also been seen. These are not retail versions. Competition This section needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (April 2010) The original MS-DOS advertisement in 1981. On microcomputers based on the Intel 8086 and 8088 processors including the IBM PC and clones the initial competition to the PC DOS/MS-DOS line came from Digital Research whose CP/M operating system had inspired MS-DOS. In fact there remains controversy as to whether Q-DOS was more or less plagiarised from early versions of CP/M code. Digital Research released CP/M-86 a few months after MS-DOS and it was offered as an alternative to MS-DOS and Microsoft's licensing requirements but at a higher price. Executable programs for CP/M-86 and MS-DOS were not interchangeable with each other; much applications software was sold in both MS-DOS and CP/M-86 versions until MS-DOS became preponderant (later Digital Research operating systems could run both MS-DOS and CP/M-86 software). MS-DOS supported the simple .COM and the more advanced relocatable .EXE executable file formats; CP/M-86 a relocatable format using the file extension .CMD. Most of the machines in the early days of MS-DOS had differing system architectures and there was a certain degree of incompatibility and subsequently vendor lock-in. Users who began using MS-DOS with their machines were compelled to continue using the version customized for their hardware or face trying to get all of their proprietary hardware and software to work with the new system. In the business world the 808x-based machines that MS-DOS was tied to faced competition from the Unix operating system which ran on many different hardware architectures. Microsoft itself sold a version of Unix for the PC called Xenix. In the emerging world of home users a variety of other computers based on various other processors were in serious competition with the IBM PC: the Apple II early Apple Macintosh the Commodore 64 and others did not use the 808x processor; many 808x machines of different architectures used custom versions of MS-DOS. At first all these machines were in competition. In time the IBM PC hardware configuration became dominant in the 808x market as software written to communicate directly with the PC hardware without using standard operating system calls ran much faster but on true PC-compatibles only. Non-PC-compatible 808x machines were too small a market to have fast software written for them alone and the market remained open only for IBM PCs and machines that closely imitated their architecture all running either a single version of MS-DOS compatible only with PCs or the equivalent IBM PC DOS. Most clones cost much less than IBM-branded machines of similar performance and became widely used by home users while IBM PCs had a large share of the business computer market. Microsoft and IBM together began what was intended as the follow-on to MS/PC DOS called OS/2. When OS/2 was released in 1987 Microsoft began an advertising campaign announcing that "DOS is Dead" and stating that version 4 was the last full release. OS/2 was designed for efficient multi-tasking an IBM speciality derived from deep experience with mainframe operating systems and offered a number of advanced features that had been designed together with similar look and feel; it was seen as the legitimate heir to the "kludgy" DOS platform. MS-DOS had grown in spurts with many significant features being taken or duplicated from Microsoft's other products and operating systems. MS-DOS also grew by incorporating by direct licensing or feature duplicating the functionality of tools and utilities developed by independent companies such as Norton Utilities PC Tools (Microsoft Anti-Virus) QEMM expanded memory manager Stacker disk compression and others. During the period when Digital Research was competing in the operating system market some computers like Amstrad PC-1512 were sold with floppy disks for two operating systems (only one of which could be used at a time) MS-DOS and CP/M-86 or a derivative of it. Digital Research produced DOS Plus which was compatible with MS-DOS 2.11 supported CP/M-86 programs had additional features including multi-tasking and could read and write disks in CP/M and MS-DOS format. While OS/2 was under protracted development Digital Research released the MS-DOS compatible DR-DOS 5 which included features only available as third-party add-ons for MS-DOS (and still maintained considerable internal CP/M-86 compatibility). Unwilling to lose any portion of the market Microsoft responded by announcing the "pending" release of MS-DOS 5.0 in May 1990. This effectively killed most DR-DOS sales until the actual release of MS-DOS 5.0 in June 1991. Digital Research brought out DR-DOS 6 which sold well until the "pre-announcement" of MS-DOS 6.0 again stifled the sales of DR-DOS. Microsoft had been accused of carefully orchestrating leaks about future versions of MS-DOS in an attempt to create what in the industry is called FUD (fear uncertainty and doubt) regarding DR-DOS. For example in October 1990 shortly after the release of DR-DOS 5.0 and long before the eventual June 1991 release of MS-DOS 5.0 stories on feature enhancements in MS-DOS started to appear in InfoWorld and PC Week. Brad Silverberg Vice President of Systems Software at Microsoft and General Manager of its Windows and MS-DOS Business Unit wrote a forceful letter to PC Week (November 5 1990) denying that Microsoft was engaged in FUD tactics ("to serve our customers better we decided to be more forthcoming about version 5.0") and denying that Microsoft copied features from DR-DOS: "The feature enhancements of MS-DOS version 5.0 were decided and development was begun long before we heard about DR-DOS 5.0. There will be some similar features. With 50 million MS-DOS users it shouldn't be surprising that DRI has heard some of the same requests from customers that we have." (Schulman et al. 1994). 7 The pact between Microsoft and IBM to promote OS/2 began to fall apart in 1990 when Windows 3.0 became a marketplace success. Much of Microsoft's further contributions to OS/2 also went in to creating a third GUI replacement for DOS Windows NT. IBM which had already been developing the next version of OS/2 carried on development of the platform without Microsoft and sold it as the alternative to DOS and Windows. Legal issues As a response to Digital Research's DR-DOS 6.0 which bundled SuperStor disk compression Microsoft opened negotiations with Stac Electronics vendor of the most popular DOS disk compression tool Stacker. In the due diligence process Stac engineers had shown Microsoft part of the Stacker source code. Stac was unwilling to meet Microsoft's terms for licensing Stacker and withdrew from the negotiations. Microsoft chose to license Vertisoft's DoubleDisk using it as the core for its DoubleSpace disk compression8. MS-DOS 6.0 and 6.20 were released in 1993 both including the Microsoft DoubleSpace disk compression utility program. Stac successfully sued Microsoft for patent infringement regarding the compression algorithm used in DoubleSpace. This resulted in the 1994 release of MS-DOS 6.21 which had disk-compression removed. Shortly afterwards came version 6.22 with a new version of the disk compression system DriveSpace which had a different compression algorithm to avoid the infringing code. Prior to 1995 Microsoft licensed MS-DOS (and Windows) to computer manufacturers under three types of agreement: per-processor (a fee for each system the company sold) per-system (a fee for each system of a particular model) or per-copy (a fee for each copy of MS-DOS installed). The largest manufacturers used the per-processor arrangement which had the lowest fee. This arrangement made it expensive for the large manufacturers to migrate to any other operating system such as DR-DOS. In 1991 the U.S. government Federal Trade Commission began investigating Microsoft's licensing procedures resulting in a 1994 settlement agreement limiting Microsoft to per-copy licensing. Digital Research did not gain by this settlement and years later its successor in interest Caldera sued Microsoft for damages. It was believed that the settlement ran in the order of $150m but was revealed in November 2009 with the release of the Settlement Agreement to be $280m.citation needed Use of undocumented APIs Microsoft also used a variety of tactics in MS-DOS and several of their applications and development tools that while operating perfectly when running on genuine MS-DOS (and PC DOS) would break when run on another vendor's implementation of DOS. Notable examples of this practice included: Microsoft's QuickPascal released in early 1989 was the first MS product that checked for MS-DOS by modifying the program's Program Segment Prefix using undocumented DOS functions and then checked whether or not the associated value changed in a fixed position within the DOS data segment (also undocumented). This check also made it into later MS products including Microsoft QuickC v2.5 Programmer's Workbench and Microsoft C v6.07. The (once infamous) AARD code a block of code in the Windows 3.1 beta installer. It was XOR encrypted self-modifying and deliberately obfuscated using various undocumented DOS structures and functions to determine whether or not Windows really was running on MS-DOS7. Note that the Windows 3.0 beta code only gave a warning that Windows would not operate properly on a "foreign" OS. It did in fact run just fine on DR-DOS 6.0. Interrupt routines called by Windows to inform MS-DOS that Windows is starting/exiting information that MS-DOS retained in an INWINDOWS flag in spite of the fact that MS-DOS and Windows were supposed to be two separate products7. End of MS-DOS In 2011 MS-DOS is still used in some enterprises to run legacy applications such as this US Navy food service management system. Today MS-DOS is rarely used for desktop computing. Since the release of Windows 95 it was integrated as a full product used for bootstrapping and troubleshooting and no longer released as a standalone product. Windows XP contains a copy of the Windows Me boot disk stripped down to bootstrap only. This is accessible only by formatting a floppy as an "MS-DOS startup disk". Files like the driver for the CD-ROM support were deleted from the Windows ME bootdisk and the startup files (AUTOEXEC.BAT and CONFIG.SYS) no longer had a content. This modified disk was the base for creating the MS-DOS image for Windows XP. Some of the deleted files can be recovered with an undelete tool9. With Windows Vista the files on the startup disk are dated 18 April 2005 but are otherwise unchanged including the string "MS-DOS Version 8 Copyright 1981-1999 Microsoft Corp" inside COMMAND.COM. However the only versions of DOS currently recognized as stand-alone OSs and supported as such by the Microsoft Corporation are DOS 6.0 and 6.22 both of which remain available for download via their MSDN volume license and OEM license partner websites for customers with valid login credentials. MS-DOS is still used in embedded x86 systems due to its simple architecture and minimal memory and processor requirements. The command line interpreter of NT-based versions of Windows cmd.exe maintains most of the same commands and some compatibility with DOS batch files. The Windows command-line interface All versions of Microsoft Windows have had an MS-DOS like command-line interface (CLI). This could run many DOS and variously Win32 OS/2 1.x and Posix command line utilities in the same command-line session allowing piping between commands. The user interface and the icon up to Windows 2000 followed the native MS-DOS interface. Consumer Windows (up to 3.11 Win9x WinME) ran as a Graphical User Interface (GUI) running on top of MS-DOS. With Windows 95 98 and ME the MS-DOS part was integrated to give the illusion of a new operating system. The command line accessed the DOS command line (usually command.com) through a Windows module (winoldap.mod). A new line of Windows (Windows NT) boot through a kernel whose sole purpose is to load Windows: there is no character-mode boot similar to Consumer Windows OS/2 or UNIX). The console runs as a Win32 session with the default processor cmd.exe being a feature-reduced version of OS/2's version. The command session permits running of various supported command line utilities from Win32 MS-DOS OS/2 1.x and POSIX. The 32-bit Windows can run MS-DOS programs through the use of the NTVDM (NT Virtual DOS Machine). This launches a stubbed version of MS-DOS 5.0. Launching any DOS application such as the DOS command processor command.com creates a 16-bit sub-system providing most of the higher level DOS APIs for DOS programs to run and even communicate with each other. The 32-bit CLI is usually referred to as the MS-DOS prompt. Although the binary interface is no longer that found in PC-DOS etc. it is an 'interface' and not an API. The commands typed here the batches etc. all resemble those of MS/PC-DOS in much the same way that the Linux/UNIX commands resemble each other without underlying binary compatibility. All versions of Windows for x86-64 and Itanium architectures no longer include the NTVDM and can therefore no longer natively run MS-DOS or 16-bit Windows applications. There are alternatives in the form of Virtual machine emulators such as Microsoft's own Virtual PC as well as VMware DOSBox and others. Legacy compatibility The option to create a MS-DOS boot disk is still present in Windows 7. From 1983 onwards various companies worked on graphical user interfaces (GUIs) capable of running on PC hardware. With DOS being the dominant operating system several companies released alternate shells e.g. Microsoft Word for DOS XTree and the Norton Shell. However this required duplication of effort and did not provide much consistency in interface design (even between products from the same company). Later in 1985 Microsoft Windows was released as Microsoft's first attempt at providing a consistent user interface (for applications). The early versions of Windows ran on top of MS-DOS and its clones. At first Windows met with little success but this was also true for most other companies' efforts as well for example GEM. After version 3.0 (1990) Windows gained market acceptance. Later versions (Windows 95 Windows 98 and Windows Me) used the DOS boot process to launch itself into protected mode. Basic features related to the file system such as long file names were only available to DOS when running as a subsystem of Windows. Windows NT ran independently of DOS but included a DOS subsystem so applications could run in a virtual machine under the new OS. With the latest Windows releases even dual-booting MS-DOS is problematic as DOS may not be able to read the basic file system. Related systems Single-user Several similar products were produced by other companies. In the case of PC DOS and DR-DOS it is common but incorrect to call these "clones". Given that Microsoft manufactured PC DOS for IBM PC DOS and MS-DOS were (to continue the genetic analogy) "identical twins" that diverged only in adulthood and eventually became quite different products. Although DR-DOS is regarded as a clone of MS-DOS the DR-DOS versions appeared months and years before Microsoft's products. (For example MS-DOS 4 released in July 1988 was followed by DR-DOS 5 in May 1990. MS-DOS 5 came in April 1991 with DR-DOS 6 being released the following June. MS-DOS 6 did not arrive until April 1993 with Novell DOS 7 DR-DOS' successor following the next month.10) What made the difference in the end was Microsoft's control of the Windows platform and their programming practices which intentionally made Windows appear as if it ran poorly on competing versions of DOS7. Both IBM (DOS 5.02) and DRI (DOS 6 update) had to release interim releases to circumvent Windows limitations inserted artificially7 designed specifically to provide Microsoft with an unfair competitive advantage7. PC DOS DR-DOS / Novell DOS / OpenDOS GNU/DOS / FreeDOS / FreeDOS 32 PTS-DOS and PowerShell. These products are collectively referred to as DOS. However MS-DOS can be a generic reference to DOS on IBM-PC compatible computers. See also Bad command or file name Comparison of x86 DOS operating systems DOSKey MS-DOS utility History of Microsoft Windows List of DOS commands List of Microsoft Windows versions Microsoft Windows MS-DOS API Timeline of x86 DOS operating systems Win32 console - a text-rendering system akin to MS-DOS 4DOS - designed to replace the default command interpreter COMMAND.COM DOSBox Quotations "IBM wanted CP/M prompts. It made me throw up." -- Tim Paterson 11 Remarks Notice that he is called the author of Dos and not the author of MS-DOS Notes Tim Paterson. "An Inside Look at MS-DOS". Seattle Computer Products. Seattle. http://www.patersontech.com/Dos/Byte/InsideDos.htm. Retrieved 2011-04-13.  "A Short History of MS-DOS". http://www.patersontech.com/Dos/Byte/History.html. Retrieved December 5 2009.  a b c d e f Conner Doug. "Father of DOS Still Having Fun at Microsoft". Micronews. http://www.patersontech.com/Dos/Micronews/paterson041098.htm. Retrieved December 5 2009.  a b Allan Roy A. (2001). "Microsoft in the 1980's part III 1980's The IBM/Macintosh era". A history of the personal computer: the people and the technology. London Ontario: Allan Pub.. p. 14. ISBN 0-9689108-0-7. http://www.retrocomputing.net/info/allan/. Retrieved December 5 2009.  http://www.emsps.com/oldtools/msdosv.htm http://pcmuseum.tripod.com/dos.htm a b c d e f g Schulman Andrew (1994). Undocumented DOS: A Programmer's Guide to Reserved MS-DOS Functions and Data Structures (2nd ed.). Addison-Wesley. ISBN 0-201-63287-X.  BYTE Magazine How Safe is Disk Compression February 1994. http://mirror.href.com/thestarman/winxp/winxpsd.htm Timeline 1980-1993 Hunter David (1983). "The Roots of DOS". Softalk for the IBM Personal Computer. http://www.patersontech.com/Dos/Softalk/Softalk.html. Retrieved 2007-06-14.  References Microsoft. MS-DOS 6 Technical Reference External links Wikibooks has a book on the topic of Basic Computing Using Windows/Appendices/Dual Booting MS-DOS Resources - Information on various aspects of MS-DOS including downloads Current License Agreement Policies for MS-DOS and Windows Tim Paterson on DOS - Paterson wrote the QDOS OS MS-DOS: A Brief Introduction Richard Bonner's DOS website Batfiles - the DOS batch file programming handbook and tutorial Arachne graphical browser for DOS MS-DOS Reference DOS version timeline Linux/dosemu Ralf Brown's Interrupt List DOS command overview DOSBox a multiplatform DOS emulator Garbo - An MS-DOS program distribution library at the University of Vaasa Finland MS-DOS 6 Technical Reference at Microsoft TechNet Promotional video for MS-DOS 5 List of all released Microsoft Operating Systems and betas v d eOperating systems by Microsoft Xenix  MS-DOS  MSX-DOS  OS/2  Windows (1.0  2.x  3.x  9x  NT  CE  Mobile)  Xbox operating system  Xbox 360 System Software  Zune  DangerOS  Singularity  Midori  Barrelfish v d eOperating system General History  Timeline  List  Comparison  Usage share  Development  Advocacy Kernel Architectures General Monolithic kernel  Microkernel Subtypes Exokernel  Nanokernel  Hybrid Components User/Kernel space  Server  Loadable kernel module  Device driver Process management Concepts Process  Process control block  Interrupt  Thread  Context switch  Scheduling CPU modes Protected mode  Supervisor mode Scheduling algorithm Cooperative multitasking  Preemptive multitasking  Round-robin scheduling  Fixed priority pre-emptive scheduling  Multilevel feedback queue  Shortest job next Memory management Memory protection  Segmentation  Paging  Segmentation fault  General protection fault  Bus error Examples AmigaOS  BeOS  BSD  DOS  GNU  Linux  Mac OS  MorphOS  OS/2  ReactOS  Solaris  Unix  Windows  more... 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