If you didn't know Microsoft used to have its own version of Unix a long time ago: Xenix. Never seen it personally though, my first experience with PC was MSDOS.
As anecdote, given the UNIX prices even for PCs, the teacher would carry a PC with Xenix into our lab and then each group would have about 20 minute turns to test what was already prepared typing on MS-DOS.
This is why getting a C compiler for MS-DOS mattered to many of us, we wanted to maximize our slot as much as possible, it wasn't about its qualities.
https://en.wikipedia.org/wiki/Xenix