It was indeed, according to The Register, thirty years ago that MS-DOS hit the market:
MS-DOS is 30 years old today. Well, kind of. On 27 July 1981, Microsoft gave the name MS-DOS to the disk operating system it acquired on that day from Seattle Computer Products (SCP), a hardware company owned and run by a fellow called Rod Brock.
SCP developed what it at various times called QDOS and 86-DOS to run on a CPU card it had built based on Intel’s 8086 processor.
