QDOS
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QDOS, the "Quick and Dirty Operating System," (not to be confused with Sinclair's QDOS for the Sinclair QL computer, which shared the same name) was a simple 16-bit operating system originally written in just four months by Tim Paterson in 1980 for an Intel 8086-based computer kit sold by Seattle Computer Products (SCP), which became famous as a part of one of the greatest legends in computer folklore.
QDOS was a 16-bit clone of the Digital Research's CP/M operating system, the most popular 8-bit operating system of the 1970s and early 1980s.
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Reasons for QDOS
QDOS was created because sales of SCP's 8086 computer kit, demonstrated in June 1979 and shipping in November, were languishing due to the absence of an operating system. The only software which SCP could propose with the board was the stand-alone Microsoft BASIC-86. Its development has been facilitated by the fact that SCP previously lent Microsoft a pre-release version of their 8086 board; Microsoft was very eager to get their software working on the new processor. They also participated in the June demo.
On the contrary, Digital Research was delaying the delivery of CP/M-86, a version of CP/M that would run on that processor. SCP did not lend a board to Digital. It is uncertain whether Digital was not interested in another board or SCP considered that it would not help Digital to progress much. SCP only had two working prototypes in house anyway.
QDOS was developed quickly, but it lacked many features of CP/M. It was marketed as 86-DOS.
IBM needs a microcomputer OS: the lost deal
In late 1980, IBM was developing what would become the original IBM Personal Computer. CP/M was by far the most popular operating system in use at the time, and IBM felt it needed CP/M in order to compete. There are at least two rumors about why IBM ended up licensing QDOS instead of CP/M.
One story is that Gary Kildall, of Digital Research and creator of CP/M (and subsequently DR-DOS) simply refused to answer the door when representatives from IBM rang his doorbell. However, the most prevalent story, and the one relayed by Bill Gates, is that when IBM approached Kildall for a license, Kildall kept the IBM executives waiting for hours while he went flying in his airplane. He missed one of the great opportunities of the century when IBM then turned to Microsoft to provide an operating system.
Neither story is generally accepted as true. By many accounts and notably according to Paterson, Kildall did not handle business negotiations and left that to his former wife, Dorothy McEwen, and attorney. Neither was willing to sign IBM's non-disclosure agreement. In addition, they refused to modify CP/M-86, and insisted on a higher royalty than IBM proposed.
IBM goes to Microsoft
As a result, IBM turned to Microsoft, since Microsoft was a CP/M subcontractor, sold a plug-in Z80 board that made the Apple II capable of running CP/M and, having ported their BASIC to SCP's bare 8086 hardware already had experience with writing OS-level code for this processor and in general. Notably, for QDOS Paterson preferred to clone BASIC's FAT filesystem rather than the original CP/M filesystem, which he perceived as inferior.
IBM asked if they could subcontract CP/M for the IBM PC. Microsoft's contract would not permit it. Instead, Microsoft purchased a nonexclusive license for QDOS—by then being marketed under the name 86-DOS—from Seattle Computer Products in December 1980 for $25,000. In May 1981, Microsoft hired Tim Paterson to port QDOS to the IBM-PC, which used the slower and less expensive Intel 8088 processor and had its own specific galaxy of peripherals around.
IBM was watching the developments daily, submitted over 300 bug reports before accepting the product and wrote the user manual for it. They also allegedly requested that everything related to the project, and notably their beta IBM PC hardware remained sealed in a single room at Microsoft.
In July 1981, a month before the PC's release, Microsoft purchased all rights to 86-DOS from SCP for 50,000 USD.
A success story
QDOS met IBM's main criteria: It looked like CP/M, and it was easy to adapt existing 8-bit CP/M programs to run under it, notably thanks to QDOS's TRANS command which would translate source files from 8080 to 8086 machine instructions. Microsoft licensed QDOS to IBM, and it became PC-DOS 1.0. This license also permitted Microsoft to sell DOS to other companies, which it did. Spectacularly successful, this deal was later challenged in court by SCP on the grounds that Microsoft had concealed its relationship with IBM in order to purchase the operating system cheaply; subsequently, there was a (1 million dollar) settlement, but no admission of duplicity or guilt.
CP/M-86 becomes irrelevant
When IBM released DOS, it sold for $60 USD, and was much more attractively priced than the $240 CP/M. Digital Research considered suing Microsoft, since DOS replicated nearly all of the CP/M system calls, program structure, and user interface (not the filesystem), but decided against it. Digital Research realized that they would have to also sue IBM, and decided that they did not have the resources to sue a company of that size, and would not likely win.
By 1982, when IBM asked Microsoft to release a version of DOS that was compatible with a hard disk, Microsoft rewrote DOS to such an extent that Digital Research had lost their opportunity to sue. PC-DOS 2.0 was an almost complete rewrite of DOS, so by March 1983, very little of QDOS remained [does not seem relevant, DOS remained backwards compatible and the claim was not on implementation]. The most enduring element of QDOS was its primitive line editor, EDLIN, which remained the only editor supplied with Microsoft versions of DOS until the June 1991 release of MS-DOS 5.0, which included a graphical editor based on QBasic.
QDOS versions
- QDOS v0.1, August 1980
- 86-DOS v0.3, December 1980
- 86-DOS v1.0, April 1981
- PC-DOS v1.0, August 1981
- PC-DOS v1.10, June 1982
- MS-DOS v1.24, June 1982
- MS-DOS v1.25, July 1982de:QDOS