This article is about IBM PC DOS. For other compatible operating systems of the DOS family, see DOS.

developer IBM and Microsoft
Programmed in Assembly Language
OS family DOS
Working state Historic
Source model Closed source
Initial release August 1981
Latest stable release PC DOS 2000 / April 1998
Supported platforms x86
Kernel type Monolithic kernel
Default user interface Command line interface
License Proprietary

IBM PC DOS (full name: The IBM Personal Computer Disk Operating System) is a DOS system for the IBM Personal Computer and compatibles, manufactured and sold by IBM from the 1980s to the 2000s. From its inception until 1993, PC DOS was a rebranded version of Microsoft MS-DOS.


The IBM task force assembled to develop the PC decided that critical components of the machine, including the operating system, would come from outside vendors. This radical break from company tradition of in-house development was the key decision that made the IBM PC an industry standard. But it was done out of necessity, to save time. Microsoft was selected for the operating system.

IBM wanted Microsoft to retain ownership of whatever software it developed, and wanted nothing to do with helping Microsoft, other than making suggestions from afar. According to task force member Jack Sams, "The reasons were internal. We had a terrible problem being sued by people claiming we had stolen their stuff. It could be horribly expensive for us to have our programmers look at code that belonged to someone else because they would then come back and say we stole it and made all this money. We had lost a series of suits on this, and so we didn't want to have a product which was clearly someone else's product worked on by IBM people. We went to Microsoft on the proposition that we wanted this to be their product."

IBM first contacted Microsoft to look the company over in July 1980. Negotiations continued over the next months, and the paperwork was officially signed in early November.[1]

Although the company expected that most customers would use DOS[2] IBM supported using CP/M-86—which became available six months after DOS[3]—or UCSD p-System as operating systems.[4] IBM was correct; one survey found that 96.3% of PCs were ordered with the $40 DOS compared to 3.4% for the $240 CP/M-86.[5]


PC DOS 1.x

Microsoft first licensed,[6] then purchased[7] 86-DOS from Seattle Computer Products (SCP), which was modified for the IBM PC by Microsoft employee Bob O'Rear with assistance from SCP (later Microsoft) employee Tim Paterson. O'Rear got 86-DOS to run on the prototype PC in February 1981. 86-DOS had to be converted from 8-inch to 5.25-inch floppy disks and integrated with the BIOS, which Microsoft was helping IBM to write.[8] IBM had more people writing requirements for the computer than Microsoft had writing code. O'Rear often felt overwhelmed by the number of people he had to deal with at the ESD (Entry Systems Division) facility in Boca Raton. 86-DOS was rebranded IBM PC DOS 1.0 for its August 1981 release with the IBM PC.

The initial version of DOS was largely based on CP/M and many of its function calls as well as the file system were copied directly from the older OS. Unlike all later DOS versions, the DATE and TIME commands were separate executables rather than part of COMMAND.COM. Single-sided 160 kilobyte (kB) 5.25" floppies were the only disk format supported.

Toward the end of 1981, Paterson went to work on an upgrade, which was called PC DOS 1.10. It debuted in May 1982 along with the Revision B IBM PC. Support for the new double-sided drives was added, allowing 320 kB per disk. A number of bugs were fixed, and error messages and prompts were made less cryptic. The DEBUG machine language monitor utility was now able to load files greater than 64k in size.

PC DOS 2.x

Later, a group of Microsoft programmers (primarily Paul Allen, Mark Zbikowski and Aaron Reynolds)[8] began work on PC DOS 2.0. Completely rewritten from the ground up, DOS 2.0 added subdirectories and hard disk support for the new IBM XT, which debuted in March 1983. A new 9-sector format bumped the capacity of floppy disks to 360 kB. The Unix-inspired kernel featured file handles in place of the CP/M-derivative file control blocks and loadable device drivers could now be used for adding hardware beyond what the IBM PC BIOS supported. BASIC and most of the utilities provided with DOS were substantially upgraded as well. A major undertaking that took almost 10 months of work, DOS 2.0 was more than twice as big as DOS 1.x, occupying around 28k of RAM compared to the 12k of its predecessor. It would form the basis for all Microsoft consumer-oriented OSes until 2001, when Windows XP (based on Windows NT) was released.[8]

The following October, DOS 2.1 debuted. Predictably a minor upgrade, it fixed some bugs and added support for half height floppy drives and the new IBM PCjr.

In 1983, newly founded Compaq released the first 100% IBM PC compatible clone and licensed their own OEM version of DOS 1.10 (quickly replaced by DOS 2.00) from Microsoft. Other PC clones followed suit, most of which included hardware-specific DOS features, but some were generic.

PC DOS 3.x

In August 1984, IBM introduced the Intel 80286-derived IBM PC/AT, its next-generation machine. Along with this was DOS 3.00. Despite jumping a whole version number, it again proved little more than an incremental upgrade, adding nothing more substantial than support for the AT's new 1.2 megabyte (MB) floppy disks. Planned networking capabilities in DOS 3.00 were judged too buggy to be usable and Microsoft disabled them prior to the OS's release. In any case, IBM's original plans for the AT had been to equip it with a proper next-generation OS that would use its extended features, but this never materialized.[1] PC DOS 3.1 (released March 1985) fixed the bugs in DOS 3.00 and supported IBM's Network Adapter card on the IBM PC Network. PC DOS 3.2 added support for 3½-inch double-density 720 kB floppy disk drives, supporting the IBM PC Convertible, IBM's first computer to use 3½-inch floppy disks, released April 1986.

In June 1985, IBM and Microsoft signed a long-term Joint Development Agreement to share specified DOS code and create a new operating system from scratch, known at the time as Advanced DOS. On April 2, 1987 OS/2 was announced as the first product produced under the agreement.[9] At the same time, IBM released its next generation of personal computers, the IBM Personal System/2 (PS/2).[1] PC DOS 3.3, released with the PS/2 line, added support for high density 3½-inch 1.44 megabyte (MB) floppy disk drives, which IBM introduced in its 80286-based and higher PS/2 models. The upgrade from DOS 3.2 to 3.3 was completely written by IBM, with no development effort on the part of Microsoft, who were working on "Advanced DOS 1.0". DOS 3.30 was the last version designed with the IBM XT and floppy-only systems in mind; it became one of the most popular versions and many users preferred it to its buggy successor.

PC DOS 4.x

PC DOS 4.0, shipped July 1988. DOS 4.0 had some compatibility issues with low-level disk utilities due to some internal data structure changes. DOS 4.0 used more memory than DOS 3.30 and it also had a few glitches. Newly added EMS drivers were only compatible with IBM's EMS boards and not the more common Intel and AST ones. DOS 4.0 is also notable for including the first version of the DOS Shell, a full screen utility designed to make the command-line OS more user friendly. Microsoft took back control of development and released a bug-fixed DOS 4.01[10]


DOS 5 debuted in June 1991. This is one of the biggest upgrades of DOS in its history. DOS 5 supported the use of the High Memory Area (HMA) and Upper Memory Blocks (UMBs) on 80286 and later systems to reduce its conventional memory usage. Also all DOS commands now supported the /? option to display command syntax. Aside from IBM's PC DOS, MS-DOS was the only other version available as OEM editions vanished since by this time PCs were 100% compatible so customizations for hardware differences were no longer necessary.

This was the last version of DOS that IBM and Microsoft shared the full code for, and the DOS that was integrated into OS/2 2.0's, and later Windows NT's, virtual DOS machine.

PC DOS 6.1

PC DOS remained a rebranded version of MS-DOS until 1993. IBM and Microsoft parted ways—MS-DOS 6 was released in March, and PC DOS 6.1 (separately developed) followed in June. Most of the new features from MS-DOS 6.0 appeared in PC DOS 6.1 including the new boot menu support and the new commands CHOICE, DELTREE and MOVE. QBasic was dropped and the MS-DOS Editor was replaced with the IBM E Editor. PC DOS 6.1 reports itself as DOS 6.00.

PC DOS 6.3

PC DOS 6.3 followed in December. PC DOS 6.30 was also used in OS/2 for the PowerPC. PC DOS 6.3 also featured SuperStor disk compression technology from Addstor.


PC DOS 7 was released in April 1995 and was the last release of DOS before IBM's Boca Raton facility closed. The REXX programming language was added, as well as support for a new floppy disk format, XDF, which extended a standard 1.44 MB floppy disk to 1.86 MB. SuperStor disk compression technology was replaced with Stac Electronics' Stacker. An algebraic command line calculator and a utility program to load device drivers from the command line were added. PC DOS 7 also included many optimizations to increase performance and reduce memory usage.

PC DOS 2000

The most recent retail release was PC DOS 2000 – released from Austin in 1998 – which found its niche in the embedded software market and elsewhere. PC DOS 2000 is a slipstream of 7.0 with Y2K and other fixes applied. To applications, PC DOS 2000 reports itself as "IBM PC DOS 7.00, revision 1", in contrast to the original PC DOS 7, which reported itself as "IBM PC DOS 7.00, revision 0".[nb 1] IBM continues to use PC DOS code to compile DOS boot disks for their servers.

ThinkPad products currently have a copy of the latest version of PC DOS in their Rescue and Recovery partition.

PC DOS 7.10

IBM produced PC DOS 7.10 which was based on PC DOS 2000 and added support for Logical Block Addressing (LBA) and FAT32 partitions. This version of DOS was never released in retail but was used in several IBM products such as the IBM ServerGuide Scripting Toolkit. This version of DOS has also appeared in Norton Ghost from Symantec. Version 7.10[nb 1] is reported to applications, since this is usually a test for support of FAT32.

Most builds of this version of DOS are limited to the kernel files IBMBIO.COM, IBMDOS.COM and COMMAND.COM. The updated programs FDISK32, FORMAT32 allow one to prepare FAT32 disks. Additional utilities are taken from PC DOS 2000, where needed.

See also



Further reading

  • IBM Corporation and Microsoft, Inc. DOS 3.30: User's Guide. IBM Corporation, 1987. Part number 80X0933.
  • IBM Corporation and Microsoft, Inc. DOS 3.30: Reference (Abridged). IBM Corporation, 1987. Part number 94X9575.
  • IBM Corporation. Getting Started with Disk Operating System Version 4.00. IBM Corporation, 1988. Part number 15F1370.
  • IBM Corporation. Using Disk Operating System Version 4.00. IBM Corporation, 1988. Part number 15F1371.
  • IBM Corporation. IBM Disk Operating System Version 5.0. User Guide and Reference. IBM Corporation, 1991. Part number 07G4584.
  • IBM Corporation. PC DOS 7 User's Guide. IBM, 1995.
  • IBM Redbooks. ISBN 0-7384-0677-5.
  • IBM Corporation. IBM PC DOS and Microsoft Windows User's Guide. Indianapolis, IN: Que Corporation, 1995. ISBN 0-7897-0276-2.

External links

  • IBM ServerGuide Scripting Toolkit - its DOS Edition contains PC DOS 7.1 (from December 2003) with LBA and FAT32 support
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