The problem that stopped SCO going head-to-head with Microsoft back in the days of Windows 3.1 and OS/2 was licensing encumbrances. AIUI, every time they sold a

The problem that stopped SCO going head-to-head with Microsoft back in the days of Windows 3.1 and OS/2 was licensing encumbrances. AIUI, every time they sold a copy of Open Desktop (the predecessor to SCO OpenServer) they had to shell out $200 to various licensees. Sun got around the problem (at least as of Solaris) by forking out $BIGNUM on a permanent license for SVR4. SCO stuck at SVR3.2 -- because by the time they knew they wanted an SVR4.x license, AT&T were wanting eye-wateringly huge license fees per copy shipped -- but did some white-room cloning work so that by 1994 or thereabouts just about the only AT&T SVR3.2 code remaining was the copyright declarations in the kernel headers: OpenServer was effectively an SVR4.2 clone. (A year or so later they actually bit the bullet and bought an SVR4.3 license ...) But rewind to 1990, in our time line. Until then, Microsoft were the junior partner in the IBM/Microsoft alliance. They'd promised to deliver a superior OS to MS-DOS, with a windowing system on top; the first couple of iterations of OS/2 were dismal, as were Windows 1 and Windows 2, but the plan was to collaborate on OS/2 2.x and then ship a next generation product, OS/2 3.0, aka "NT". As it happened, Microsoft gambled on NT while IBM stuck with OS/2, thinking that they still owned the market. But if we back up to 1987, before OS/2 1.0 shipped, the UNIX-on-PC codebase was clearly a better platform for a multi-tasking OS, and MS-DOS backward compatability could be supplied via VP-IX (if I'm remembering SCO's DOS-box's name properly). If we posit that Microsoft retained Xenix and decided to develop UNIX further, the only question is whether Bill would have coughed for an unlimited AT&T license, just as Sun did. And I think -- given MS's history of buying up the IP they needed in order to hit a marketing requirement (and remembering that I'm an outsider, so this opinion is worth exactly what you paid for it :) -- they might well have done so.