Definitions of QDOS

Definitions of QDOS

QDOS (stands for Quick and Dirty Operating System according to ABBREVIATIONFINDER) was an operating system purchased by Microsoft the company Seattle Computer and served to create the basis for what would later be PC -DOS and MS-DOS.


QDOS was created because sales of the Seattle Computer Products (SCP) 8086 Computer Kit, introduced in June 1979 and distributed in November, were declining due to the absence of an operating system. The only software that SCP could sell with the board was the standalone Microsoft BASIC-86, which Microsoft had developed into a prototype of SCP’s hardware. SCP wanted to offer the version of CP / M for 8086 that Digital Research (DRI) had announced, but its release date was uncertain. This was not the first time that DRI had lagged more than hardware development; two years earlier it had been late in adapting CP / M for the new floppy and hard disk formats. In April 1980 SCP assigned, at age 22, Tim Paterson to develop QDOS as a substitute for CP / M-86.

Paterson designed QDOS with the same internal API and most of the CP / M user commands. It did not reproduce the CP / M file system, but instead used the FAT file system supported by some versions of Microsoft BASIC. Paterson chose not to keep file system information in memory (cache) but to update it on disk with each operation. Although this option was slower, this approach avoided the need to force an update to a disk before removing it. Paterson also introduced a more English-like set of commands, such as the “COPY” utility, instead of PIP, which is more general, but less intuitive.

IBM interest

In the late 1980s, IBM was developing what would become the IBM PC. CP / M was the most popular operating system of the time and IBM believed it necessary to have a competitive system. Representatives from IBM visited Digital Research and discussed the license terms with Dorothy McEwen Kildall, Digital’s licensing representative, who was hesitant to sign the IBM contract as it contained a nondisclosure clause. Although they finally accepted the clause, Digital rejected IBM’s proposal that offered to pay it $ 250,000 in exchange for the authorization to sell all the copies that were necessary, insisting on the model of remuneration based on royalties per copy. In later conversations between IBM and Bill Gates, he mentioned the existence of QDOS and the IBM representative, Jack Sams, asked him to obtain a license for this operating system.

Creation of PC-DOS

Microsoft purchased a non-exclusive license for 86-DOS from Seattle Computer Products in December 1980 for $ 25,000. In May 1981, Tim Paterson was hired 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 observed the progress on a daily basis and submitted more than 300 change requests before accepting the product and writing the user manual for it.

In July 1981, a month before the PC was released, Microsoft bought all the rights to 86-DOS from SCP for $ 50,000. This met the main IBM criteria: It looked like CP / M and it was easy to adapt existing 8-bit CP / M programs to work under it, mostly thanks to the TRANS command in QDOS, which allowed the source code of the Intel 8080 to be translated into the language. 8086 machine code.

Microsoft licensed QDOS to IBM, and it became PC-DOS 1.0. This license also allowed Microsoft to sell DOS to other companies, which it did. The deal was spectacularly successful, and SCP later sued in court that Microsoft had covered up its relationship with IBM to buy the cheap operating system (even though Microsoft was still under the terms of a nondisclosure agreement and the PC’s degree of success was not. was widely anticipated). SCP ultimately received a million dollars as a payment agreement.

Intellectual property dispute

When DRI founder Gary Kildall examined PC-DOS and found that it duplicated the CP / M programming interface, he tried to sue IBM, which at the time claimed that PC-DOS was its own product. However, the lawyer for Digital Research did not believe that the relevant law was clear enough to make the claim (he now says he would have made the claim under current laws). However, Kildall confronted IBM and convinced them to offer CP / M-86 with the PC in exchange for a release from liability.

The controversy has continued because of the similarity between the two systems. Perhaps the most sensational claim comes from Jerry Pournelle, who claimed that Kildall personally demonstrated to him that DOS contained CP / M code (by entering a command in DOS it displayed Kildall’s name). Until 2006 Pournelle has not disclosed the command and no one has gone ahead to corroborate his story. A book from 2004 about Kildall it says that he used an encrypted message to prove that other manufacturers had copied the CP / M, but does not say that he found the message in MS-DOS; instead, his memory (a source for the book) pointed to the well-known similarity of the interface. Paterson insists that the QDOS software was his original work, and has denied referring to or otherwise using the CP / M code while writing it. After the book was published in 2004, he sued the authors and publishers for defamation. The case dates back to a lawsuit filed by Paterson against Evans in 2004, after the latter wrote in his book They Made America (They built America) that the supposed inventor of DOS – who later sold it to Bill Gates and served as the basis for his Windows operating system – had actually taken up the idea of ​​CP / M (Control Programming Monitor).

Before 1982, when IBM asked Microsoft to release a version of DOS that was compatible with a hard disk, PC-DOS 2.0 was a nearly complete rewrite of DOS, so before March 1983, there was very little of QDOS left. The most robust element of QDOS was its primitive command-line editor, EDLIN, which remained the only editor provided in Microsoft’s versions of DOS until MS-DOS version 5.0 was released in June 1991, which included a full screen editor (known as edit) based on QBasic.

Technical characteristics

Paterson designed it with the same application programming interface (API) and most of the CP / M system user commands. He modified the way diskettes were recorded using a cache memory, which accelerated the use but forced the user to update (unmount) the diskette before removing it, this was done through a specific command. He modified the name of the copy command to Copy, more intuitive for the user, and incorporated the names of the devices and the communication ports to the file system, in this way, a “copy” could be made to the printer, or to the screen, facilitating the user their tasks. This feature was retained in MS-DOS. The system was single task, single user, and used the FAT file system to maintain compatibility.


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