I just came across a 1995 post from Gordon Letwin, early Microsoft employee and lead architect of OS/2, about the history of OS/2. There are a few paragraphs in it about Microsoft and UNIX. Here's Letwin's post:
And the UNIX-related paragraphs:
It's extremely hard to do development work on an operating system when someone else controls the standard. "Control" in this case is a matter of public perception. For example, Microsoft was once very big in the Unix world. In fact, we considered it our candidate for the future desktop operating system, when machines got powerful enough to run something good. We were the worlds biggest seller of Unix systems. DOS was, when we first wrote it, a one-time throw-away product intended to keep IBM happy so that they'd buy our languages.
The UNIX contracts were all done when Bell Labs was regulated and couldn't sell Unix into the commerical marketplace. So although they wrote it and were paid royalties, they couldn't develop it in competition to us. But after a few years that changed. Bell was degregulated and now they were selling Unix directly, in competition to us! They might sell it for cheaper than we had to pay them in royalties! But that wasn't the real killer, the real killer was the Bell now controlled the standard. If we wrote an API extension that did X, and Bell wrote an incompatible one that did Y, which one would people write for? The ISVs know that AT&T was a very big company and that they'd written the original, so they'd believe that AT&T controlled the standard, not MS, and that belief would then define reality. So we'd always just be waiting for what AT&T announced and then frantically trying to duplicate it.
Bill Gates knew, right away, that there was no strong future in Unix for us any more. Fortunately at that time, DOS was taking off and we were learning, along with everyone else, about the power of standards. So the primary OS team - the Unix guys - joined with the secondary OS team - the DOS guys - and the earliest versions of OS/2 were born. (This was before IBM came on board, so it wasn't called OS/2!)
Marc Rochkind