The name MS-DOS is 30 years old today. A fledgling outfit called Microsoft emerged from the Primordial slime and repackaged a disk operating system it bought from an outfit called Seattle Computer Products.
SCP was a hardware company owned and run by a bloke called Rod Brock. Before that Brock had been developing something he either called QDOS and 86-DOS, which he had been using to run on a CPU card based on Intel's 8086 processor.
SCP had released the card in November 1979 and it shipped with an 8086-compatible version Microsoft's Basic language interpreter. SCP decided it had to create its own OS for the card which it did in August 1980. QDOS stood for Quick and Dirty Operating System and it was written by Tim Paterson.
But the problem was that QDOS was a bit too much like Digital Research CP/M OS, but since it was supposed to be a stop gap while CP/M-86 was being developed that did not matter too much.
A young and freshly scrubbed Bill Gate showed up and paid SCP $25,000 for a licence to market and sell 86-DOS. What Gates did not tell SCP is that he had a deal with IBM to supply the operating system for the hardware giant's first personal computer. However, he never told SCP and Paterson that he had a deal in the works with Big Blue until it acquired the OS.
Gates, with his idea of IBM's plans and a belief that it would make shedloads of money, bought the software outright from SCP, for a further $50,000. SCP was allowed to continue to offer the OS with its own hardware. Paterson joined Microsoft.
The 27 July, 1981 is the day that Paterson gives for the handing over of the operating system, and the name was changed and released the next day. In August 1981, Big Blue released the IBM PC based on the OS and the rest was history.