DOS was a bit of an oddity, in that you could buy it from either Microsoft or IBM. The two were never quite identical, but were always mostly interchangeable. The differences grew larger at version 6, but they were still more alike than different. Let’s take a look at PC DOS vs MS-DOS.
IBM and Microsoft collaborated on DOS, and both had the right to market it. IBM sold its version as PC DOS, while Microsoft sold its version as MS-DOS. And for a time, IBM was happy just to sell PC DOS to owners of true-blue IBM PCs. But in 1993 it changed.

David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.










