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Tracing the History of the Computer MS-DOS


MS-DOS is a disk operating system made by Microsoft. It was the dominant operating system for the PC compatible platform during the 1980s. It has gradually been replaced on consumer desktop computers with various generations of the Windows operating system.

MS-DOS was originally released in 1981 and had eight major versions released before Microsoft stopped development in 2000. It was the key product in Microsoft's growth from a programming languages company to a diverse software development firm, providing the company with essential revenue and marketing resources.


MS-DOS was created by computer manufacturer Seattle Computer Products (SCP) in 1980 as QDOS (for Quick and Dirty Operating System), but was renamed 86-DOS because it was designed to run on the Intel 8086 processor. In a sequence of events that would later inspire much folklore, Microsoft licensed QDOS to IBM on behalf of SCP. Microsoft acquired the system for only $50,000 from SCP shortly before the PC's release.


IBM and Microsoft both released versions of DOS; the IBM version was supplied with the IBM PC and known as PC-DOS. Originally, IBM only validated and packaged Microsoft developments, and thus IBM's versions tended to be released shortly after Microsoft's. However, MS-DOS 4.0 was actually based on IBM PC-DOS 4.0, as Microsoft was by then concentrating on OS/2 development. Microsoft released its versions under the name "MS-DOS", while IBM released its versions under the name "PC-DOS". Initially, when Microsoft would license their OEM version of MS-DOS, the computer manufacturer would customize its name (i.e. TandyDOS, Compaq DOS, etc). Most of these versions were identical to the official MS-DOS; however, Microsoft began to insist that OEMs start calling the product MS-DOS. Eventually, only IBM resisted this move.

Computer advertisements of this period often claimed that computers were "IBM-Compatible" or very rarely "MS-DOS compatible". The two terms were not synonyms. There were computers which used MS-DOS which could not run all the software that an IBM-Compatible machine could. An example is the Pivot, which used MS-DOS but was not IBM-Compatible.

Programs written specifically for IBM compatibles could run faster by bypassing slow MS-DOS functions, e.g. by writing video information directly to the area of memory assigned to it.


MS-DOS grew in spurts, with many significant features being taken from other products and operating systems, such as Microsoft's own Xenix - a variant on Unix - and Digital Research's DR-DOS, as well as tools and utilities including Norton Utilities, PC Tools (Microsoft Anti-Virus), QEMM expanded memory manager, Stacker disk compression, and so on.

With Intel's introduction of the 80286 microprocessor, IBM and Microsoft began work on a joint project called OS/2, originally a protected-mode version of MS-DOS. Later, Microsoft abandoned the project to devote full resources to Windows and Windows NT. Digital Research created the GEM graphical user interface (GUI), which had little popularity on PC compatibles. It was very successful on the Atari ST machines, but was ultimately eclipsed by Microsoft's Windows 3.0 release.

Although its role as a desktop computer operating system has greatly diminished, today it is still used in various embedded x86 systems due to its simplistic architecture, minimal memory requirements, and minimal processor speed requirements.

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. Stac was unwilling to meet Microsoft's terms for licensing Stacker and withdrew from the negotiations. In the due diligence process, Stac engineers had shown Microsoft some Stacker source code.

Soon, MS-DOS 6.0 was released, 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 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, rewritten to avoid the infringing code.

These tactics were common for Microsoft; the company lost another lawsuit resulting from code in Windows 3.1 which caused spurious errors when Windows was launched on DR-DOS.

Prior to 1995, Microsoft licensed MS-DOS 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 1994 the US government charged Microsoft with violations of antitrust law, and a settlement agreement limited Microsoft to per-system licensing. Digital Research did not gain by this settlement, and years later its successor in interest Caldera sued Microsoft for damages. This lawsuit was settled with a monetary payment of 150 million dollars.


MS-DOS was not designed to be a multi-user or multitasking operating system, but many attempts were made to retrofit these capabilities. The Terminate and Stay Resident (TSR) system call (originally targeted at loadable device drivers) and other mostly-undocumented functions were used to create pop-up applications. Although it used them itself, Microsoft discouraged use and sometimes denied the existence of these undocumented functions, but as many classes of co-resident software required these features developers were forced to disassemble MS-DOS to create their products. Borland's SideKick personal productivity product was a notable specimen. Add-on environments like TopView and especially DESQview attempted to provide multitasking, and achieved some success when later combined with the virtual 8086 mode and virtual memory features of the Intel 80386 and later processors. Windows/386 2.1 and subsequent versions provided similar albeit poorer features when running in "386 enhanced" mode, but Microsoft never specifically marketed this possibility and was mostly interested in converting customers to using GUI-mode Windows applications.

User interface

MS-DOS employs a command line interface and a batch scripting facility via its command interpreter, MS-DOS was designed so users could easily substitute a different command line interpreter, for example 4DOS.

Beginning with version 4.0, MSDOS included a file manager program with a quasi-graphical user interface (the DOS Shell) that featured menus, split windows, and program shortcuts using character mode graphics that were a primitive imitation of the Mac OS and Windows.

MS-DOS compatibility with other Microsoft operating systems

After the release of the Apple Macintosh in 1984, IBM personal computer users also desired a graphical user interface. Many programs running under MS-DOS tried to fill the void by creating their own graphical interface, such as 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 product lines). Non-Microsoft efforts to provide a consistent interface, for example, Digital Research's GEM, also failed.

Early versions of Microsoft Windows were ordinary programs that ran on top of MS-DOS and its clones. Later versions were launched from DOS but "extended" it by going into protected mode. Still later versions of MS Windows ran independently of DOS but included much of the old code such that DOS could run in virtual machines under the new OS. In new computers, MS-DOS cannot run directly if the hard drive uses the NTFS file system, which is the recommended file system in Windows XP. Users who wish to access their NTFS-formatted hard drive must use a NTFS compatible version of DOS.

Related systems

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; DR-DOS was a clone of itself once removed.

Under Linux it is possible to run copies of DOS and many of its clones under dosemu, a Linux-native virtual machine for running real mode programs. There are a number of other emulators for running DOS under various versions of UNIX, even on non-x86 platforms.


MS-DOS Timeline

This article is derived from

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