Re: @misc. folks talking about Xenix ...
"SCO may have done the work but Microsoft paid them to do it."
No. SCO paid MS to have access to the source that MS licensed from MaBell.
Microsoft tried to make it their own after it actually started being used by all and sundry, but MS never actually did any coding on/for Xenix. All MS did was use a resale license for MaBell's code.