1) Microsoft existed before IBM gettiong the OS contract with IBM. About 5 1/2 years, in fact. 2) Wasn't really a question of Big Blue being lazy. The PC development team were specifcally tasked with getting the PC to market as quickly as possible, and decided to source various components, including the OS, from outside vendors to achieve this. What they really wanted was CP/M, which they tried to commission from Digital Research. And what they ended up with was 86-DOS, which was API compatible with CP/M 3) DOS never stood for Dirty Operating System. QDOS (which later became 86-DOS), however, did stand for Quick and Dirty Operating System, but you can't extract just the DOS from there, out of context.