86-DOS, known internally and in official documents as QDOS, Q-DOS, Seattle DOS, and SCP-DOS,[1] is an operating system developed by Seattle Computer Products that was later licensed[2] and then bought[3] by Microsoft and used as the basis for IBM PC-DOS and MS-DOS.
Development of QDOS began in April 1980 out of the growing need for an 8086 operating system,[4] as CP/M-86 had been delayed since December 1979.[5][6] It was written on a Cromemco Z80 computer[7] running Cromemco's CDOS, in a text editing software called MicroPro WordMaster.[8][9] It was then translated using a Z80 to 8086 translator called TRANS-86 (which was later ported to 86-DOS and renamed to simply TRANS)[8][10] and tested on the Seattle Computer Products 16-bit Computer System.[11] QDOS was ready to ship in July, with Tim Paterson, the creator, spending about half of his time on its development.[4][12] Though the operating system wasn't completely finished, Paterson figured a quick release was more important than adding all the features.[13]
Though some parts of QDOS were written from scratch or by referencing the CP/M-80 manual,[14] others were created in Z80 assembly and then translated using the TRANS command.[15] Paterson claims that QDOS was created with CP/M translation compatibility being the goal[16] - however, these extreme similarities between the OSes caused controversy,[a] even going as far as a defamation case.[b] It has also been rumored that QDOS' development was aided by not only the CP/M manuals, but the source code as well[17] (or even Digital Research's original OEM translation tools).[18] However, these rumors are both unsourced and unlikely.[c]
Paterson later revealed he had mostly worked on hardware before QDOS, and that the idea came during his work on Seattle Computer products' 8086 board.[6] He decided on aspects of the OS because of his experience with North Star and Cromemco's variants of CP/M,[5] UCSD p-System, and Unix.[8][d] He also took inspiration for the filesystem from an unfinished 8-bit operating system known as Microsoft Interrupt Driven Asynchronous System (MIDAS[15] or M-DOS,[19] called MDOS before 1980[e]), written by Marc McDonald,[15][19] which he learned about during the 1979 National Computer Conference.[8]
↑Perhaps the most compelling argument comes from the creator of CP/M, Gary Kildall - "Ask Bill why function code 6 (in DOS) ends with a dollar sign. ... No one in the world knows that but me." (quoted directly from Bill Gates: Of Mind and Money by James Wallace and Jim Erickson, published in the 8 May 1991 issue of Seattle Post-Intelligencer) Tim Paterson would later respond to this in Document 14-2 of the case Paterson v. Little, Brown, and Co., et al., reasoning that the name was in the CP/M manual he had.
↑The only way Seattle Computer Products could have had the CP/M source code or OEM translation tools was if they had a source code license from Digital Research - that too has also been rumored, though it is once again unsourced and not very likely.
↑While uncited as an influence in the creation of QDOS, Paterson had also used CDC SCOPE, Cromemco RDOS, and the IMSAI 8080 Self-Contained System. (From Document 14-2 of Paterson v. Little, Brown, and Co., et al.)
↑The exact date of the name change is unknown, but drafts of the user manual from 1979 and 1980 give an approximate date.
↑ 15.015.115.2Manes, Stephen; Andrews, Paul (1993). Gates: How Microsoft's Mogul Reinvented an Industry—and Made Himself the Richest Man in America. Doubleday. p. 280-281. ISBN 0-385-42075-7.