"The story begins unambiguously. A group of IBMers, working on a secret project to build a personal computer, flew to Seattle in August, 1980, to see if [Bill] Gates could supply them with an operating system. He couldn't -- and referred them to [Gary] Kildall [of Digital Research Inc.] When they showed up at DRI's offices the next day ... the company's business manager ... refused to sign their nondisclosure agreement.... [IBM] did get together with Kildall ... a short time later, but they couldn't reach an agreement. At around the same time, [IBM] saw Gates again. [IBM] and Gates both knew of the operating system [Tim] Paterson had built at Seattle Computer Co.... "Gates said: 'Do you want to get [QDOS], or do you want me to?' [IBM] said: 'By all means, you get it."' Gates bought Paterson's program, called QDOS, for $50,000, renamed it DOS, improved it, and licensed it to IBM for a low per-copy royalty fee."
Tim Paterson, the man who created DOS, the operating system that dominated the computer industry between 1981 and 2000, has an occasional blog
that provides a fascinating history of the microcomputer industry: Is DOS a Rip-Off of CP/M?
; The Contributions of CP/M
; Design of DOS
; The First DOS Machine
; IBM PC Design Antics
; and All Those Floppy Disk Formats…
Programmers Who Defined The Technology Industry: Where Are They Now?