@Colin Brett (was: @Dave Mundt_
"Wasn't Xenix a Microsoft OS?"
No. Xenix was actually licensed by Microsoft from AT&T in the late 1970s. From what I remember it was the standard PDP11 Version 7 Unix source code, un-modified by Microsoft. SCO ported it to the IBM PC's 8086/8088 architecture in roughly 1983. Most of us yawned ... although looking back, it was a pretty good hack by SCO!
Before SCO's port was released, there was a TRS-68000 version, a Zilog Z8001 port, and an Altos 8086 version (not necessarily in that order). Microsoft didn't write any of them, rather the third-party companies in question did the coding. Seems to me I once saw an Apple Lisa running Xenix, not certain who did that port. Can anyone jog my memory?
For more on my take on *real* SCO, see these posts: