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PC DOS (IBM DOS)

150px
A typical command line in PC DOS.
Company / developer	IBM and Microsoft
OS family	DOS
Working state	Historic
Source model	Closed source
Initial release	August 1981
Latest stable release	PC DOS 2000 / 1998
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.

The DOS INT 21h function 30h get DOS version returns OEM code 00h for IBM instead of FFh for Microsoft. This is relevant for DOS 7, because various features introduced in MS DOS 7 (a part of Windows 95) are not supported in PC DOS 7, and vice versa, e.g., MS DOS 7 does not support REXX, and PC DOS 7 does not support FAT32.

History[link]

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]

Versions[link]

PC DOS 1.x[link]

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. 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.^[2] 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.

DOS 1.00[link]

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 160k 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 320k 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[link]

Later, a group of Microsoft programmers (primarily Paul Allen, Mark Zbikowski and Aaron Reynolds)^[2] 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 360k. 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 consumer Microsoft OSes until 2001.^[2]

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 completely generic.

PC DOS 3.x[link]

In August 1984, IBM introduced the 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 1.2MB 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. DOS 3.2 became the first version sold by Microsoft in a generic retail edition while all previous DOSes were OEM releases sold only with new PCs.

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.^[3] At the same time, IBM released its next generation of personal computers, the IBM Personal System/2.^[1] PC DOS 3.3, released with the PS/2 line, added support for high density 3½-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[link]

PC DOS 4.0, shipped July 1988. DOS 4.0's kernel was heavily rewritten. The OS proved to have numerous glitches^{[citation needed]} in it in addition to taking more than twice as much memory^{[citation needed]} as DOS 3.30. Newly-added EMS drivers were only compatible with IBM's EMS boards and not the more common^{[citation needed]} Intel and AST ones. IBM also stripped out support for the obsolete DOS 1.x file control blocks, but this caused numerous complaints^{[citation needed]} from people running older applications (especially WordStar). 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 4.1^[4]

PC DOS 5[link]

Digital Research released a retail DOS 5.0, which caught Microsoft off-foot, but the combination of vaporware, and some hurried coding, allowed Microsoft to stave off the competition. This DOS also is the last 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. DOS in these operating systems for the i386 computer never progressed past this.^{[citation needed]}

The original 1987 joint development agreement by IBM and Microsoft had envisioned two next-generation OSes; OS/2 (developed by the former) would be a high end professional OS and Windows (developed by the latter) was to be a smaller, cheaper, and less advanced one for home and school use. However, relations between the two companies gradually deteriorated, especially in the wake of the DOS 4.0 debacle. Microsoft instead decided to develop Windows into a full-fledged competitor to OS/2 instead of its junior partner. In 1990, Windows 3.0 debuted, which had full protected mode support and advanced 32-bit features that the 16-bit OS/2 lacked. IBM finally responded with OS/2 2.0 in 1992, a powerful 32-bit OS that offered capabilities beyond those of Windows. However, they were fighting a losing battle and after a brief tug of war with Windows 3.1, OS/2 faded into irrelevance.

Under the terms of the split, IBM was allowed to keep (and buy the rights for) their own DOS, which they did. They were allowed to keep Win-OS/2 as well (basically Windows 3.10 for OS/2). Microsoft was rather specific on what DOS was, since OEM diskettes were labeled "MS-DOS and Additional Tools", i.e. two products. IBM released their own DOS, with a new editor, and a number of utilities being full back-versions of PC-Tools. Microsoft's tools were feature-limited Norton tools.

Meanwhile, MS-DOS 5.0 debuted in April 1991. Designed with Windows and 32-bit PCs in mind, it was the biggest upgrade of DOS since 2.0. Advanced memory management tools were included to allow the use of protected mode software, and the old 1981-vintage BASICA/GW-BASIC and EDLIN were replaced by the modernized QBASIC and DOS Editor. Aside from IBM's PC-DOS, MS DOS was the only version and OEM editions vanished. Microsoft also restored file control block support in DOS 5.0.

PC DOS 6.1[link]

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. QBasic was dropped and the MS-DOS Editor was replaced with E.

MS-DOS 6.0 (released March 1993) added further new features such as the MSCDEX utility for CD-ROMs and modernized disk and backup programs.

PC DOS 6.3[link]

MS-DOS 6.2 (October 1993) added mostly minor upgrades and dropped some outdated utilities.

PC DOS 6.3 followed in December. PC DOS 6.30 was also used in OS/2 for the PowerPC.

The final split came after DOS 6.30. One notes that 6.30 has the improvements that 6.20 has, and that beginning with 6.22 and Windows 3.11, the preferred server OS switched from OS/2 to Windows NT.

The last standalone DOS version was MS-DOS 6.22 (released May 1994). Otherwise identical to DOS 6.2, it resulted from an embarrassing lawsuit when Microsoft was found to have stolen Stax Electronics's patented disk compression technology, resulting in a brief DOS 6.21 version that had no compression utility included. DOS 6.22 replaced DBLSPACE with DRVSPACE, a similar disk compression utility licensed from Central Point Software.

PC DOS 7.0[link]

PC DOS 7.0 was released in November 1994. 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.

IBM's DOS 7.0, the last released before Boca Raton closed, included more SAA features (like REXX, IPF view for help, and unpack2 - all out of OS/2), along with removing the incorrect DOS version from most, but not all of the utilities.

PC DOS 2000[link]

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 basically 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 7.0, which reported itself as revision 0. 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.^{[citation needed]}

PC DOS 7.10[link]

IBM produced PC-DOS 7.10, based on the PC-DOS 2000 source, and features to support LBA and FAT32 drives, to assist making servers and restore environments for computers and laptops. This provides support for the larger hard disks. This version of DOS has also appeared in Norton Ghost from Symantec. Version 7.10 is returned to applications, since this is usually a test for support of FAT32.

Most builds of this DOS are limited to the kernel files IBMBIO.COM, IBMDOS.COM and COMMAND.COM. Additional utilities are taken from PC-DOS 2000, where needed. REXX utilities run from batch files.

Programs like FDISK32, FORMAT32 allow one to prepare fat32 disks.

PC-DOS 7.10 supports booting to the hard drive, when no key is pressed. This is useful in a setup condition, when the first boot is off an diskette image on the cd-rom, but the second boot must be from the hard drive. Left unattended, the boot passes from the cd-rom via IBMCDET.SYS, to the hard drive, in the same manner that Windows 9x JO.SYS and Windows NT fixboot.bin do.

'NOINT25.COM' hides the old DOS Int25 disk read interface. Windows 98 chkdsk will not run if this is present.

See also[link]

• Timeline of x86 DOS operating systems
• Comparison of x86 DOS operating systems
• List of DOS commands

References[link]

Further reading[link]

• 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. PC DOS 7 Technical Update. IBM, 1995. 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[link]

• ftp://ftp.boulder.ibm.com/software/dos/ PC DOS 2000 (Chinese Edition), freely available for download from IBM
• IBM ServerGuide Scripting toolkit - its DOS Edition contains PC DOS 7.1 (June 2005) with LBA and FAT32 support