Comment by pdonis

I was being somewhat sloppy. IBM bought DOS from Microsoft for the IBM PC--but neglected to buy exclusive rights to it, so Microsoft could and did sell it on its own as MS-DOS. (And later, other vendors began selling their own versions.) For PC users, this was a great deal, since it effectively made the IBM PC an open standard. But it meant that IBM captured much less value from DOS and PCs than Microsoft did.