QDOS

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This article is about the predecessor of MS-DOS. For the Sinclair QL operating system, see Sinclair QDOS.

**QDOS**
Company/ developer:	Tim Paterson
OS family:	DOS
Source model:	Closed source
Latest stable release:	0.1 / August 1980
Default user interface:	CLI
License:	Proprietary
Working state:	Historic

QDOS, the "Quick and Dirty Operating System," 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
6 References
7 External links

[edit] Origins

QDOS was created because sales of SCP's 8086 computer kit, demonstrated in June 1979 and shipped 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. SCP had contacted DR about obtaining a 8086 version of CP/M, but DR founder and software manager Gary Kildall had no interest in 16-bit systems. In April 1980 Paterson started developing QDOS as a substitute for CP/M.

Paterson designed QDOS with the same internal API and most of the user commands of CP/M. As MS-DOS, QDOS lost some of the legacy commands of CP/M. The PIP file copy subsystem, similar to that used on DEC minicomputers was replaced by the COPY command. Instead of having to run PIP, then type dest=source, then exit, the MS-DOS command is simply copy source dest, similar to the copy command in VAX/VMS which succeeded the PDP-11 operating systems. Another feature of CP/M which inconvenienced users was the need to hit a control key to register a floppy disk whenever the disk was changed. Future versions of DOS and Windows would adopt features similar to Unix and GUI operating system shell and user interfaces.

The first version, marketed as 86-DOS, was finished very quickly but lacked many CP/M features. Paterson did not clone CP/M's file system, but used the FAT filesystem supported by some versions of Microsoft BASIC.

[edit] 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. IBM's representatives visited Digital Research and discussed licensing with Kildall after he returned from a business errand. However, Kildall remained uninterested in 16-bit technology. According to some versions of the story, Digital Research also rejected IBM's offer to license CP/M for a one-time sum of $250,000, rather than the usual royalties plan.^[1]

With no operating system for the PC, IBM asked Bill Gates of Microsoft whether he could port the system under the license he had obtained for the Z-80 SoftCard. Gates could not, but he nonetheless promised IBM a CP/M compatible operating system.

[edit] 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 watched 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.

[edit] Intellectual property dispute

When IBM released DOS, it sold for $60 USD, and so was much more attractively priced than the (as yet undelivered) $240 CP/M. Digital Research considered suing Microsoft, since DOS replicated nearly all of the CP/M system calls, program structure, and user interface, 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 (known as edit) based on QBasic.