Microsoft BOUGHT DOS from Seattle Computer Products in 1980 for $50,000! Just in time to license it en-mass on IBM PCs.
Accidental Empires by Robert X. Cringely, pp. 132-133
Wow, you hit upon one of the biggest secrets in IT history. I always heard, though, that Gates "appropriated" the DOS code from it's original inventor and then used licensing trickery to keep him down while he started making his millions selling MS-DOS.
Please correct me if I'm wrong.