PC-DOS

IBM PC-DOS was one of three major operating systems that dominated the personal computer market from about 1985 to 1995. The original 1981 arrangement between IBM and Microsoft was that Microsoft would provide the base product and that both firms would work on developing different parts of it into a more powerful and robust system, and then share the resultant code. MS-DOS and PC DOS were to be marketed separately: IBM selling to itself for the IBM PC, and Microsoft selling to the open market. ThinkPad products currently have a copy of the latest version of PC DOS in their Rescue and Recovery partition.

PC-DOS and MS-DOS

For many years MS-DOS and PC DOS were so nearly identical that most people tended to confuse them, and a program written for either one could be virtually guaranteed to work equally well on the other. It is commonplace to see people write "MS-DOS was the operating system for the original IBM PC", but the IBM PC companion product was actually PC DOS in the traditional IBM blue wrapper. Other companies also produced their own branded DOS versions: mostly just MS-DOS under licence from Microsoft, but the MS-DOS based Compaq DOS included significant customisation, notably with version 3.31 which was the most advanced DOS on the market for quite some time (if we ignore the CP/M-86 and DR-DOS family of products).

For DOS versions 1 through 5, the differences between MS-DOS and PC DOS remained trivial. After the release of DOS 5.0, however, IBM and Microsoft, until then the closest of allies, had a serious falling out. The primary issue was the future of more advanced operating systems—Microsoft favoring Windows because it was easier to market and they owned one hundred percent of it and IBM favoring the much more ambitious and technically sophisticated joint IBM–Microsoft project OS/2—but the ramifications for the IBM–Microsoft business relationship were broader. From this time on, MS-DOS and PC DOS would diverge, and for the first time, IBM would start actively marketing PC DOS to other computer manufacturers and to the public at large.

IBM PSP (their Personal Software Products arm) aimed to make sure that PC DOS remained one jump ahead of its better-known competitor in the version number race. After MS-DOS 6.0 was released, the then-beta PC DOS 6.0 was released as PC DOS 6.1. Soon after, MS-DOS 6.0 ran into stability problems and had to be upgraded, becoming MS-DOS 6.2. A lawsuit prompted Microsoft to release a version without DoubleSpace, which was 6.21 and then Microsoft developed DriveSpace, which does not use the infriging technology and included it in the final version, 6.22. In response, IBM updated PC DOS to version 6.3, which was to become the best-known and most successful version. A substantial number of smaller PC manufacturers switched to PC DOS at this time, particularly those that grew tired of waiting for the long-promised update to the now-ancient DR-DOS 6.0 from Digital Research/Novell.

The last competition of the DOS wars came with the more-or-less simultaneous release of PC DOS 7.0 and Novell DOS 7.0. The general expectation was that Novell's feature-rich product would prove superior and more successful: the reality was that PC DOS was substantially more reliable and easier to configure than either of its competitors, and usually cheaper too. In the short term, PC DOS looked like a winner.

Windows

In the meantime, end users and software developers shifted from DOS to Windows, which became an operating system of its own, and, since the introduction of 32-bit File Access in version 3.11, was merely using DOS as a boot loader. The next release, Windows 95, introduced long file names through the VFAT file system, which required modifying all MS-DOS utilities to support this feature. Hypothetically, it was still possible to start Windows from a non-Microsoft version of DOS, but then during the Windows session, the foreign DOS utilities would not see long file names and consequently could not preserve them during writing operations. Windows 95 still allowed dual-booting with MS-DOS on the same disk partition, whether a Microsoft or competing release, but it made little sense to the user and could destroy long file names. For example, OS/2 3.0 would automatically run the CHKDSK utility during installation and destroy the Windows 95 long file names.

The final release, PC DOS 2000, found its niche in the embedded software market and elsewhere. This version dealt with the Year 2000 problem. Versions 7 and 2000 supported a diskette format known as XDF, which allowed for more data to be written to a standard floppy disk than usual.

Versions

Some information about previous versions:

IBM PC-DOS 2.0 fit on two 160K 5.25-inch floppy diskettes, (single-sided DD 360K) and was copyrighted in 1983. Maximum disk partition native to OS: 10MB.
IBM PC-DOS 3.2 required 128KB RAM, fit on one 720KB DSDD diskette, had file dates 12/30/1985. COMMAND.COM is 23,791 bytes and the box says the operating system was sold "As-Is". Maximum disk partition native to OS: 32MB.
PC-DOS 4.01 fit on two 3.5-inch DD diskettes (720K) and required 256KB (360KB with SHELL option). The operating system file COMMAND.COM is 37,637 bytes. Maximum disk partition native to OS: 2000MB.

Image:PC DOS 3 2 box.gif Image:PC DOS 4 getting started.gif Image:IBM pc dos5.gif

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PC-DOS and MS-DOS

Windows

Versions

See also