MS-DOS
In August 1980, Seattle Computer Products shipped the first version of an operating system called 86-DOS. Tim Paterson wrote this software in just six weeks to run on Intel 8086 processors. The code was essentially a clone of Digital Research's CP/M but included improved disk sector buffering and introduced the FAT12 file system. Microsoft needed an operating system for its upcoming deal with IBM. Bill Gates hired Tim Paterson in May 1981 and purchased 86-DOS 1.10 that July for fifty thousand dollars. Microsoft kept the original version number but renamed the product MS-DOS. They licensed MS-DOS 1.10 to IBM, which released it as PC DOS 1.0 in August 1981 for the IBM Personal Computer. Within one year, Microsoft had licensed MS-DOS to over seventy other companies. This strategy allowed any computer using an 8086-family processor to run the same software. Early versions relied heavily on floppy disks for storage because hard drives were rare and expensive at the time.
Version 2.0 arrived in October 1983 and became the first release to support double-sided 360 KB 5.25-inch floppy disks. It also introduced user-installable device drivers and a tree-structure filing system. Version 3.0 followed in April 1985 and added support for 1.2 MB floppy drives along with FAT16 partitions up to 32 MB. By November 1987, version 3.31 supported partitions larger than 32 MiB and reached up to 512 MB. The 4.00 release in October 1988 brought built-in support for hard disk partitions up to 2 GB and included EMS drivers for 386-compatible processors. Version 5.0 released in May 1991 introduced the HIMEM.SYS driver to load portions of the operating system into upper memory areas. This allowed programs to use more conventional memory. MS-DOS 6.0 came out in 1993 and included online help through QBasic plus disk compression utilities. The final standalone retail version was 6.22 from 1994. Versions 7 and 8 existed only as background components within Windows 9x systems.
Digital Research released CP/M-86 shortly after MS-DOS but at a higher price point. Executable programs for the two systems were not interchangeable during the early years. Microsoft faced competition again when Digital Research launched DR-DOS 5.0 in May 1990. Brad Silverberg, Vice President of Systems Software at Microsoft, wrote a letter to PC Week on the 5th of November 1990 denying that his company used fear tactics against competitors. He claimed feature enhancements for MS-DOS 5.0 began long before they heard about DR DOS 5.0. Sales of DR-DOS dropped significantly after Microsoft announced the pending release of MS-DOS 5.0 in May 1990. Actual sales resumed only after MS-DOS 5.0 shipped in June 1991. Digital Research later released DR-DOS 6.0 which sold well until Microsoft pre-announced MS-DOS 6.0. This effectively killed most DR-DOS sales once more. Stac Electronics sued Microsoft over patent infringement regarding the DoubleSpace compression algorithm included in MS-DOS 6.0 and 6.20. The lawsuit resulted in the 1994 release of version 6.21 without disk compression. Version 6.22 followed with DriveSpace using a different algorithm to avoid infringing code.
Windows 3.0 launched in 1990 and marked the beginning of the end for command-line driven MS-DOS. Early versions of Windows ran as a graphical user interface on top of MS-DOS. With the release of Windows 95, the role of MS-DOS was reduced to that of a boot loader according to Microsoft. MS-DOS programs could still run in a virtual DOS machine within 32-bit Windows. Version 7.0 appeared inside Windows 95's first retail release and contained support for VFAT long file names. Version 7.1 arrived with Windows 98 Second Edition and added support for the FAT32 file system. It also introduced logical block addressing. Windows Me removed the capability to boot its underlying MS-DOS 8.0 alone from a hard disk. This change meant users could no longer access the command line directly during startup unless they used an emergency boot floppy. The VER internal command reported version numbers like 4.00.950 or 4.10.1998 depending on the specific Windows build. Applications through the API would report version 7.00 or 7.10 instead.
Microsoft declared all versions of MS-DOS 6.22 and older obsolete on the 31st of December 2001. Support ended when Windows 95 extended support concluded on that same date. Later versions tied to Windows 98 and ME lost support on the 11th of July 2006. Sixty-four-bit versions of Windows NT prior to Windows 11 dropped DOS emulation entirely. Windows 11 removed the NTVDM component which had been present in earlier systems. This effectively ended any association between MS-DOS and Microsoft Windows after thirty-six years. MS-DOS 6.22 remains available for download via MSDN websites for customers with valid login credentials. Some embedded x86 systems still use MS-DOS due to its simple architecture and minimal memory requirements. In 2018, Microsoft released source code for MS-DOS 1.25 and 2.0 on GitHub. The purpose was mainly for education and experimentation with historic operating systems. Program manager Rich Turner stated other versions could not be open-sourced due to third-party licensing restrictions. Users are allowed to fork the repository containing the source code and make their own modifications.
Common questions
When did Microsoft acquire 86-DOS and rename it to MS-DOS?
Microsoft purchased 86-DOS 1.10 in July 1981 after hiring Tim Paterson in May 1981. The company kept the original version number but renamed the product MS-DOS before licensing it to IBM.
What features did MS-DOS 2.0 introduce when it arrived in October 1983?
MS-DOS 2.0 became the first release to support double-sided 360 KB 5.25-inch floppy disks. It also introduced user-installable device drivers and a tree-structure filing system.
Why did Digital Research lose sales of DR-DOS 5.0 compared to MS-DOS 5.0?
Sales of DR-DOS dropped significantly after Microsoft announced the pending release of MS-DOS 5.0 in May 1990. Actual sales resumed only after MS-DOS 5.0 shipped in June 1991, and later releases were killed by pre-announcements from Microsoft.
How did Windows 95 change the role of MS-DOS as a boot loader?
With the release of Windows 95, the role of MS-DOS was reduced to that of a boot loader according to Microsoft. Version 7.0 appeared inside Windows 95's first retail release and contained support for VFAT long file names.
When did Microsoft declare all versions of MS-DOS 6.22 and older obsolete?
Microsoft declared all versions of MS-DOS 6.22 and older obsolete on the 31st of December 2001. Support ended when Windows 95 extended support concluded on that same date.