IBM PC DOS, an

acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...

for IBM Personal Computer Disk Operating System, is a discontinued disk operating system for

IBM PC compatible IBM PC compatible computers are similar to the original IBM Personal Computer, IBM PC, IBM Personal Computer XT, XT, and IBM Personal Computer/AT, AT, all from computer giant IBM, that are able to use the same software and expansion cards. Such ...

s. It was manufactured and sold by IBM from the early 1980s into the 2000s. Developed by

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...

, it was also sold by that company 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 ope ...

. Both operating systems were identical or almost identical until 1993, when IBM began selling PC DOS 6.1 with new features. The collective shorthand for PC DOS and MS-DOS was

DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...

, 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 business magnate and philanthropist. He is a co-founder of Microsoft, along with his late childhood friend Paul Allen. During his career at Microsoft, Gates held the positions ...

, 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 Jack may refer to: Places * Jack, Alabama, US, an unincorporated community * Jack, Missouri, US, an unincorporated community * Jack County, Texas, a county in Texas, USA People and fictional characters * Jack (given name), a male given name, ...

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 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 University of California, San Diego (UCS ...

operating systems. IBM's expectation proved correct: one survey found that 96.3% of PCs were ordered with the PC DOS compared to 3.4% with the 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 TopView is the first object-oriented, multitasking, and windowing, personal computer operating environment for PC DOS developed by IBM, announced in August 1984 and shipped in March 1985. TopView provided a text-mode (although it also ran in gr ...

for DOS to Microsoft so that Microsoft could more fully understand how to develop an

object-oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of p ...

operating environment In computer software, an operating environment or integrated applications environment is the environment in which users run application software. The environment consists of a user interface provided by an applications manager and usually an app ...

, overlapping windows (for its development of Windows 2.0) and multitasking.

Versions

PC DOS 1.x

Microsoft first licensed, then purchased 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 Tim Paterson (born 1 June 1956) is an American computer programmer, best known for creating 86-DOS, an operating system for the Intel 8086. This system emulated the application programming interface (API) of CP/M, which was created by Gary ...

. 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, or a diskette) is an obsolescent 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 wi ...

and integrated with the BIOS, 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. 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 uni ...

'' 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 Rebranding is a marketing strategy in which a new name, term, symbol, design, concept or combination thereof is created for an established brand with the intention of developing a new, differentiated identity in the minds of consumers, investors ...

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 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

. 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 digital information. The International System of Units (SI) defines the prefix '' kilo'' as 1000 (103); per this definition, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quant ...

(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 utility 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 Paul Gardner Allen (January 21, 1953 – October 15, 2018) was an American business magnate, computer programmer, researcher, investor, and philanthropist. He co-founded Microsoft Corporation with childhood friend Bill Gates in 1975, which ...

, 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 The IBM Personal Computer XT (model 5160, often shortened to PC/XT) is the second computer in the IBM Personal Computer line, released on March 8, 1983. Except for the addition of a built-in hard drive and extra expansion slots, it is very simila ...

, 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, multiuser 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, an ...

-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 hav ...

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 upgrade to its predecessors, Windows 2000 for high-end and ...

(based on

Windows NT Windows NT is a proprietary graphical operating system produced by Microsoft, the first version of which was released on July 27, 1993. It is a processor-independent, multiprocessing and multi-user operating system. The first version of Win ...

) 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 (sometimes abbreviated to CQ prior to a 2007 rebranding) was an American information technology company founded in 1982 that developed, sold, and supported computers and related products and services. Compaq produced ...

released the Compaq Portable, 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 ...

-derived

IBM PC/AT The IBM Personal Computer/AT (model 5170, abbreviated as IBM AT or PC/AT) was released in 1984 as the fourth model in the IBM Personal Computer line, following the IBM PC/XT and its IBM Portable PC variant. It was designed around the Intel 80 ...

, 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. 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 The IBM PC Convertible (model 5140) is a laptop computer made by IBM, first sold in April 1986. The Convertible was IBM's first laptop-style computer, following the luggable IBM Portable, and introduced the 3½-inch floppy disk format to the IB ...

, 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 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 r ...

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 discontinued in MS-DOS version 6.22, but remained part of the Supplemental Disk. The Supplemental Disk could be ordered or could be do ...

, 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 In DOS memory management, the high memory area (HMA) is the RAM area consisting of the first 65520 bytes above the one megabyte in an IBM AT or compatible computer. In real mode, the segmentation architecture of the Intel 8086 and subsequen ...

(HMA) and Upper Memory Blocks (UMBs) on 80286 and later systems to reduce its

conventional memory In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the read-write memory directly addressable by the processor for use by the operating system ...

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 Virtual DOS machines (VDM) refer to a technology that allows running 16-bit/32-bit DOS and 16-bit Windows programs when there is already another operating system running and controlling the hardware. Overview Virtual DOS machines can operate eit ...

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

was dropped and the

MS-DOS Editor __NOTOC__ MS-DOS Editor, commonly just called ''edit'' or ''edit.com'', is a TUI text editor that comes with MS-DOS 5.0 and later, as well as all "x86" SKUs of Windows, until Windows 11. It supersedes edlin, the standard editor in earlier versi ...

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 6.3 was also used in OS/2 for the PowerPC. 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 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 mustard) is moving at velocities comparable to that of the moving fluid, relative to the ambient fluid through which the object is churning. The term sli ...

of 7.0 with

Y2K The year 2000 problem, also known as the Y2K problem, Y2K scare, millennium bug, Y2K bug, Y2K glitch, Y2K error, or simply Y2K refers to potential computer errors related to the formatting and storage of calendar data for dates in and after ...

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". Hitachi 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 computers and tablets designed, developed and marketed by Lenovo, and formerly by IBM until 2005, when IBM's PC business was acquired by Lenovo. ThinkPads have a distinct black, boxy design la ...

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 address ...

(LBA) and

FAT32 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

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 Ghost (an acronym for ''general hardware-oriented system transfer'') is a disk cloning and backup tool originally developed by Murray Haszard in 1995 for Binary Research. The technology was acquired in 1998 by Symantec. The backup and recove ...

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 file In computer science, a record-oriented filesystem is a file system where data is stored as collections of records. This is in contrast to a byte-oriented filesystem, where the data is treated as an unformatted stream of bytes. There are several ...

s 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 transaction management and connectivity for applications on IBM mainframe systems under z/OS and z/VSE. CICS family products ...

. 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.