IBM PC DOS (an

acronym An acronym is a type of abbreviation consisting of a phrase whose only pronounced elements are the initial letters or initial sounds of words inside that phrase. Acronyms are often spelled with the initial Letter (alphabet), letter of each wor ...

for IBM Personal Computer Disk Operating System),Formally known as "The IBM Personal Computer DOS" from versions 1.0 through 3.30, as reported in those versions' respective COMMAND.COM outputs also known as PC DOS or IBM DOS, is a discontinued

disk operating system A disk operating system (DOS) is a computer operating system that requires a disk or other direct-access storage device as secondary storage. A DOS provides a file system and a means for loading and running computer program, programs stored on th ...

for the

IBM Personal Computer The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible ''de facto'' standard. Released on August 12, 1981, it was created by a ...

, its successors, and

IBM PC compatible An IBM PC compatible is any personal computer that is hardware- and software-compatible with the IBM Personal Computer (IBM PC) and its subsequent models. Like the original IBM PC, an IBM PC–compatible computer uses an x86-based central p ...

s. It was sold by

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

from the early 1980s into the 2000s. Developed by

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

, it was also sold by that company to the open market as

MS-DOS MS-DOS ( ; 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 op ...

. Both operating systems were identical or almost identical until 1993, when IBM began selling PC DOS 6.1 with its own new features. The collective shorthand for PC DOS and MS-DOS was DOS, which is also the generic term for disk operating system, and is shared with dozens of disk operating systems called DOS.

History

The IBM task force assembled to develop the IBM 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 one of the key decisions that made the IBM PC an industry standard.

, founded five years earlier by

Bill Gates William Henry Gates III (born October 28, 1955) is an American businessman and philanthropist. A pioneer of the microcomputer revolution of the 1970s and 1980s, he co-founded the software company Microsoft in 1975 with his childhood friend ...

, was eventually 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 months that followed, and the paperwork was officially signed in early November. Although IBM expected that most customers would use PC DOS, the IBM PC also supported CP/M-86, which became available six months after PC DOS, and

UCSD p-System UCSD Pascal is a Pascal (programming language), Pascal programming language system that runs on the UCSD p-System, a portable, highly machine-independent operating system. UCSD Pascal was first released in 1977. It was developed at the Universit ...

operating systems. IBM's expectation proved correct: one survey found that 96.3% of PCs were ordered with the $40 PC DOS compared to 3.4% with the $240 CP/M-86. Over the history of IBM PC DOS, various versions were developed by IBM and Microsoft. By the time PC DOS 3.0 was completed, IBM had a team of developers covering the full OS. At that point in time, either IBM or Microsoft completely developed versions of IBM PC DOS going forward. By 1985, the joint development agreement (JDA) between IBM and Microsoft for the development of PC DOS had each company giving the other company a completely developed version. Most of the time branded versions were identical, but there were some cases in which each of the companies made minor modifications to their version of DOS. In the fall of 1984, IBM gave all the source code and documentation of the internally developed IBM TopView for DOS to Microsoft so that Microsoft could more fully understand how to develop an object-oriented operating environment, overlapping windows (for its development of Windows 2.0) and multitasking.

Version history

Versions

PC DOS 1.x

Microsoft first licensed, then purchased

86-DOS 86-DOS (known internally as QDOS, for Quick and Dirty Operating System) is a discontinued operating system developed and marketed by Seattle Computer Products (SCP) for its Intel 8086-based computer kit. 86-DOS shared a few of its commands wi ...

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 A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a ...

and integrated with the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

, which Microsoft was helping IBM to write. 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, Florida Boca Raton ( ; ) is a city in Palm Beach County, Florida, United States. The population was 97,422 in the 2020 United States census, 2020 census and it ranked as the 23rd-largest city in Florida in 2022. Many people with a Boca Raton Address, ...

. Perhaps the first public mention of the operating system was in July 1981, when ''

Byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...

'' discussed rumors of a forthcoming personal computer with "a CP/M-like DOS ... to be called, simply, 'IBM Personal Computer DOS. 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-80 1.x and most of its architecture, function calls and file-naming conventions were copied directly from the older OS. The most significant difference was the fact that it introduced a different file system, FAT12. Unlike all later DOS versions, the and commands were separate executables rather than part of . Single-sided 160

kilobyte The kilobyte is a multiple of the unit byte for Computer data storage, digital information. The International System of Units (SI) defines the prefix ''kilo-, kilo'' as a multiplication factor of 1000 (103); therefore, one kilobyte is 1000&nbs ...

(KB) 5.25-inch floppies were the only disk format supported. In late 1981, Paterson, now at Microsoft, began writing 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 was now able to load files greater than 64 KB in size.

PC DOS 2.x

Later, a group of Microsoft programmers (primarily Paul Allen, Mark Zbikowski and Aaron Reynolds) began work on PC DOS 2.0. Completely rewritten, 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 Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

-inspired kernel featured

file handle In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically ha ...

s in place of the CP/M-derivative file control blocks and loadable device drivers could now be used for adding hardware beyond that which 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 28 KB of RAM compared to the 12 KB of its predecessor. It would form the basis for all Microsoft consumer-oriented OSes until 2001, when

Windows XP 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 successor to Windows 2000 for high-end and business users a ...

(based on

Windows NT Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Original ...

) was released. In October 1983 (officially 1 November 1983) DOS 2.1 debuted. It fixed some bugs and added support for half-height floppy drives and the new IBM PCjr. In 1983,

Compaq Compaq Computer Corporation was an American information technology, information technology company founded in 1982 that developed, sold, and supported computers and related products and services. Compaq produced some of the first IBM PC compati ...

released the

Compaq Portable The Compaq Portable is an early portable computer which was one of the first IBM PC compatible systems. It was Compaq Computer Corporation's first product, to be followed by others in the Compaq Portable series and later Compaq Deskpro series. ...

, the first 100%

and licensed their own OEM version of DOS 1.10 (quickly replaced by DOS 2.00) from Microsoft. Other PC compatibles followed suit, most of which included hardware-specific DOS features, although some were generic.

PC DOS 3.x

In August 1984, IBM introduced the

Intel 80286 The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non- multiplexed address and data buses and also the f ...

-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 The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes ...

(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. 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 -inch double-density 720 KB floppy disk drives, supporting the IBM PC Convertible, IBM's first computer to use -inch floppy disks, released April 1986, and later the

IBM Personal System/2 The Personal System/2 or PS/2 is IBM's second generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART (serial p ...

in 1987. 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 2 April 1987

OS/2 OS/2 is a Proprietary software, proprietary computer operating system for x86 and PowerPC based personal computers. It was created and initially developed jointly by IBM and Microsoft, under the leadership of IBM software designer Ed Iacobucci, ...

was announced as the first product produced under the agreement. At the same time, IBM released its next generation of personal computers, the

(PS/2). PC DOS 3.3, released with the PS/2 line, added support for high density -inch 1.44 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 (internally known as DOS 3.4 originally) 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 DOS Shell is a file manager that debuted in MS-DOS and PC DOS version 4.0, released in June 1988. It was no longer included in MS-DOS version 6, but remained part of the Supplemental Disk. The Supplemental Disk could be ordered or could b ...

, 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.

PC DOS 5

DOS 5 debuted in June 1991. 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. The POWER.EXE was introduced that has the APM standard in version 5.02.IBM PC DOS 5.02
/ref> 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 , , and .

QBasic QBasic is an integrated development environment (IDE) and BASIC interpreter, interpreter for a variety of dialects of BASIC which are based on QuickBASIC. Code entered into the IDE is compiled into an intermediate representation (IR), and this ...

was dropped and the MS-DOS Editor was replaced with the IBM E Editor. It also licensed components of Central Point's PC Tools, such as Central Point Backup Utility (CPBACKUP). PC DOS 6.1 reports itself as DOS 6.00.

PC DOS 6.3

PC DOS 6.3 followed in December. PC DOS 6.3 was also used in OS/2 for the

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

. PC DOS 6.3 also featured SuperStor disk compression technology from Addstor.

PC DOS 7

PC DOS 7 was released in April 1995 and was the last release of DOS before IBM software development (other than the development IBM ViaVoice) moved to Austin. The

REXX Rexx (restructured extended executor) is a high-level programming language developed at IBM by Mike Cowlishaw. Both proprietary and open-source software, open source Rexx interpreter (computing), interpreters exist for a wide range of comput ...

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 Embedded software is computer software, written to control machines or devices that are not typically thought of as computers, commonly known as embedded systems. It is typically specialized for the particular hardware that it runs on and has tim ...

market and elsewhere. PC DOS 2000 is a

slipstream A slipstream is a region behind a moving object in which a wake of fluid (typically air or water) is moving at velocities comparable to that of the moving object, relative to the ambient fluid through which the object is moving. The term slips ...

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". PC-DOS 2000 was the last version of IBM PC-DOS that was sold at retail. IBM advertised it as a Y2K compliant DOS. As it reports itself as "IBM PC-DOS 7 Revision 1", it is often referred to as "IBM PC-DOS7R1" or just "PC-DOS7R1".

Hitachi () is a Japanese Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1910 and headquartered in Chiyoda, Tokyo. The company is active in various industries, including digital systems, power and renewable ener ...

used PC DOS 2000 in their legacy ''Drive Fitness Test'' (4.15) and ''Hitachi Feature Tool'' (2.15) until 2009.

ThinkPad ThinkPad is a line of business-oriented laptop and Tablet computer, tablet computers produced since 1992. It was originally designed, created and manufactured by the American IBM, International Business Machines (IBM) Corporation. IBM Acquisit ...

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

PC DOS 7.1

PC DOS 7.1 added support for

Logical Block Addressing Logical block addressing (LBA) is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disk drives. LBA is a particularly simple linear addressin ...

(LBA) and FAT32 partitions. Various builds from 1999 up to 2003 were not released in retail, but used in products such as the IBM ServerGuide Scripting Toolkit. A build of this version of DOS appeared in Norton Ghost from Symantec. Version 7.1 indicates support for FAT32 also in

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

PC DOS as a distributed file client

In 1986, IBM announced PC DOS support for client access to the file services defined by

Distributed Data Management Architecture Distributed Data Management Architecture (DDM) is IBM's open, published software architecture for creating, managing and accessing data on a remote computer. DDM was initially designed to support record-oriented files; it was extended to support ...

(DDM). This enabled programs on PCs to create, manage, and access record-oriented files available on IBM System/36, IBM System/38 and IBM mainframe computers running

CICS IBM CICS (Customer Information Control System) is a family of mixed-language application servers that provide online business transaction management, transaction management and connectivity for applications on IBM mainframe systems under z/OS ...

. In 1988, client support for stream-oriented files and hierarchical directories was added to PC DOS when they became available on the DDM server systems.