I did not know all of that history.

My exposure to early UNIX is limited to having read Cliff Stoll's "The Cuckoo's Egg" about 17 yrs ago.

Unix (and its I direct adopted child Linux) is very different than most other operating systems before and after. In that it is nearly completely portable. It’s not a stable OS, but a large pile of inter working tools.
Part of what killed the AT$T lawsuit was how quickly something can be removed and replaced.
Today everything in major use is POSIX. Including a good chunk of Windows 10/11 beyond the subsystem layers.
Check our older books like The Unix Wars or newer papers like You GNU Me.

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