[jech]

> I’m aware of alternate mainframe OSs but I’m not sure how common using one was.

Extremely common at major universities and research centres. CTSS, ITS, TENEX, Multics, Unix and even VM/370 were all alternate operating at some point.

> Other than OS2, alternate OSs for other systems were rather rare,

You weren't there, were you? A lot of people replaced MS-DOS with DR-DOS before Microsoft deliberately broke it with Windows. A little later, a number of people were running Unix System V on their PCs, to the extent that there was a regular column about Unix in Byte.

[code_duck]

Didn’t Microsoft somehow ruin Dr DOS? Not technically, but didn’t they sue them or something? Which would mean this is the same issue, 40 years later. Yes, I was there on the 80s, but I had a Commodore 64. We did use GEOS, if that counts. I was not present for the 70s.

[jech]

> Didn’t Microsoft somehow ruin Dr DOS?

They added some obfuscated code to Windows 3.1 that made it refuse to run on DR-DOS. https://en.wikipedia.org/wiki/AARD_code

[rTX5CMRXIfFG]

> at major universities and research centres

So not common outside of ivory towers, no?

[nerdsniper]

That was a huge fraction of computing at the time. Before 1992 or so, the only people I was aware of that was into computers were all associated with a University. Typewriters were still actually very common.

[tliltocatl]

Before IBM PC computer's weren't particularly commonplace outside of ivory towers either.

[LocalH]

You're forgetting the big three, all of which predated the 5150 PC - Commodore PET, Apple II, and TRS-80.

[cestith]

I went to a regional state university. We had an older IBM mainframe with a hypervisor and the students and faculty were all users on MUSIC/OS. This was in the early/mid 1990s.