@marcan Detail disagreement: "if X crashed it had a high chance of making your whole machine unusable".
No, that really isn't true. I was using X11 on BSD from 1988, on System V.4 from 1989, on UnixWare from (I think) 1992, and on Linux from 1993. I don't recall X crashing on the BSD or System V.4 at all. on Linux, X was pretty flaky in those days and crashed not infrequently; on UnixWare it did crash, but not often. I don't recall any X crash that locked the machine.
@simon_brooke @marcan my observation here is that βmaking your whole machine unusableβ is true iff the machine is essentially single-user and all of the applications/programs running on it are connected to the X server. Which is probably more likely true for the average Linux user than on more traditional Unices which more often had separation between compute server and display server.
Am now trying to remember the last time I had a unix account with uid > 1000 β¦