QDOS

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Template:Infobox OS 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 had a command structure and application programming interface that imitated that of Digital Research's CP/M operating system, which made it easy to port programs from the latter.

1 Origins
2 IBM interest
3 Creation of PC-DOS
4 Intellectual property dispute
5 QDOS versions

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Origins

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 had 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 and participated in the June demo.

Digital Research was the supplier of CP/M, the major operating system for microcomputers, and did not have a 16-bit version of CP/M in 1980. SCP did not lend a development 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. Without an available operating system, Paterson began working on QDOS in April, 1980.

Paterson designed QDOS with the same API and user commands as CP/M. His first version, marketed as 86-DOS, was finished very quickly but lacked many CP/M features. He did not clone CP/M's file system, but used the FAT filesystem supported by some versions of Microsoft BASIC.

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IBM interest

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 several speculations 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 the creator of CP/M, Gary Kildall, at Digital Research 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 an accurate account. According to Paterson and others, Kildall did not handle business negotiations and left that to his wife, Dorothy McEwen, an attorney. Paterson said she was unwilling to sign IBM's non-disclosure agreement, but Kildall associate Gordon Eubanks said she did sign it. Eubanks says that Kildall was working on a PL/1 compiler and was not interesting at the time in porting CP/M to a 16-bit processor. IBM thus turned to Microsoft, which was already providing the ROM BASIC interpreter for the PC, and Microsoft offered to provide an operating system as well.

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Creation of PC-DOS

Microsoft purchased a nonexclusive license for 86-DOS from Seattle Computer Products in December 1980 for $25,000. In May 1981, it 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 family of peripherals. IBM was watching the developments daily, submitted over 300 bug reports before accepting the product and wrote the user manual for it.

In July 1981, a month before the PC's release, Microsoft purchased all rights to 86-DOS from SCP for $50,000. It 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. The deal was spectacularly successful, and SCP later claimed in court that Microsoft had concealed its relationship with IBM in order to purchase the operating system cheaply (even though disclosing the relationship would have violated IBM's NDA). SCP ultimately received a 1 million dollar settlement payment.

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Intellectual property dispute

When IBM released DOS, it sold for $60 USD, and so 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, PC-DOS 2.0 was an almost complete rewrite of DOS, so by March 1983, very little of QDOS remained. 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.

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