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History of MS-DOS

By:  Leven Antov

Development of MS-DOS and PC-DOS began in October 1980, when IBM began searching the market for an operating system for the yet-to-be-introduced IBM PC.

IBM had originally intended to use Digital Research's (actually, they had the somewhat pretentious name of "Intergalactic Digital Research" at the time) CP/M was then the industry standard operating system - you either ran a BASIC with disk functions, someone's proprietary OS, or CP/M.

Folklore reports various stories about the rift between DRI and IBM. The most popular story claims Gary Kildall or DRI snubbed the IBM executives by flying his airplane when the meeting was scheduled. Another story claims Kildall didn't want to release the source for CP/M to IBM, which would be odd, since they released it to other companies. One noted industry pundit claims Kildall's wife killed the deal by insisting on various contract changes. I suspect the deal was killed by the good ol' boy network. It's hard to imagine a couple of junior IBM executives giving up when ordered to a task as simple as licensing an operating system from a vendor. It wouldn't look good on their performance reports. It would be interesting to hear IBM's story...

IBM then talked to a small company called Microsoft. Microsoft was a language vendor. Bill Gates and Paul Allen had written Microsoft BASIC and were selling it on punched tape or disk to early PC hobbyists, which was probably a step up from the company's original name and goal - they were Traf-O-Data before, making car counters for highway departments.

Microsoft had no 8086 real operating system to sell, but quickly made a deal to license Seattle Computer Products' 86-DOS operating system, which had been written by Tim Paterson earlier in 1980 for use on that company's line of 8086, S100 bus micros. 86-DOS (also called QDOS, for Quick and Dirty Operating System) had been written as more or less a 16-bit version of CP/M, since Digital Research was showing no hurry in introducing CP/M-86. Paterson's DOS 1.0 was approximately 4000 lines of assembler source.

This code was quickly polished up and presented to IBM for evaluation. IBM found itself left with Microsoft's offering of "Microsoft Disk Operating System 1.0". An agreement was reached between the two, and IBM agreed to accept 86-DOS as the main operating system for their new PC. Microsoft purchased all rights to 86-DOS in July 1981, and "IBM Personal Computer DOS 1.0" was ready for the introduction of the IBM PC in October 1981. IBM subjected the operating system to an extensive quality-assurance program, reportedly found well over 300 bugs, and decided to rewrite the programs. This is why PC-DOS is copyrighted by both IBM and Microsoft.

It is sometimes amusing to reflect on the fact that the IBM PC was not originally intended to run MS-DOS. The target operating system at the end of the development was for a (not yet in existence) 8086 version of CP/M. On the other hand, when DOS was originally written the IBM PC did not yet exist! Although PC-DOS was bundled with the computer, Digital Research's CP/M-86 would probably have been the main operating system for the PC except for two things - Digital Research wanted $495 for CP/M-86 (considering PC-DOS was essentially free) and many software developers found it easier to port existing CP/M software to DOS than to the new version of CP/M. The IBM PC shipped without an operating system.

IBM didn't start bundling DOS until the second generation AT/339 came out. You could order one of three operating systems for your PC, assuming you popped for the optional disk drive and 64k RAM upgrade (base models had 16k and a cassette player port). These operating systems were IBM Personal Computer DOS 1.0, a version of the UCSD p-System, which was an integrated Pascal operating system something like the souped-up BASIC operating systems used by the Commodore 64 and others, or Digital Research's CP/M-86, which was officially an option although you couldn't buy it until later. Since IBM's $39.95 DOS was far cheaper than anyone else's alternative, darned near everyone bought DOS.

Microsoft Press' "MSDOS Encyclopedia" shows a reproduction of a late DOS 1.25 OEM brochure. Microsoft was touting future enhancements to 1.25 including Xenix-compatible pipes, process forks, and multitasking, as well as "graphics and cursor positioning, kanji support, multi-user and hard disk support, and networking." Microsoft certainly thought big, but, alas, the forks, multitasking, and multiuser support never came about, at least in US versions of DOS. Oddly, the flyer claims:

"MS-DOS has no practical limit on disk size. MS-DOS uses 4-byte XENIX OS compatible pointers for file and disk capacity up to 4 gigabytes."

Umm... yeah. One sort of gets the idea nobody at Microsoft had a hard disk larger than 32 megabytes...

86-DOS February 1981 Paterson's Quick'n'Dirty DOS first runs on IBM's wirewrapped PC prototype
PC-DOS 1.0 August 1981 original IBM release
PC-DOS 2.0 March 1983 for PC/XT, Unix-type subdirectory support, installable device drivers, I/O redirection, subdirectories, hard disk support, handle calls
PC-DOS 3.0 August 1984 1.2 meg drive for PC/AT, some new system calls, new external programs, 16-bit FAT, specific support for IBM network
MS-DOS 4.0 April 1986 multitasking (Europe only) - withdrawn from market after a very short run
PC-DOS 3.3 April 1987 for PS/2 series, 1.44 meg support, multiple DOS partition support, code page switching, improved foreign language support, some new function calls, support for the AT's CMOS clock
PC-DOS 4.0 August 1988 32mb disk limit officially broken, minor EMS support, more new function calls, enhanced network support for external commands. PCjr support dropped.
MS-DOS 5.0 June 1991 high memory support, uses up to 8 hard disks, command line editor and aliasing, 2.88mb floppies, ROMable OEM kit available.
MS-DOS 6.0 March 1993 disk compression (Doublespace), multiple configurations in CONFIG.SYS

Copyright © 1996 Leven Antov

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