It’s the same situation as game consoles. Custom built hardware that is only meant to run the one specific vendor OS. There have been many other computing devices like that in the past as well. The general purpose desktop computer that allows a choice of operating systems is actually less common than the other way. Historically, people didn’t expect to run alternate operating systems on a mainframe, 80s and 90s computers like a Commodore 64, Power PC Macs, Amigas and DOS/Windows machines until Linux came along.
That’s odd, because I remember being a user of MUSIC on the university System/360. I imagine it also sounds odd to all those people who ran AT&T Unix on their PDP/11 systems instead of a Digital OS like RTS/11. Or the people who ran Xenix on their PCs. Or the folks like me who installed OS/2 on what was sold as an MS-DOS machine. Then there were the folks who ran A+ on their Atari.
Oh yeah, odd. Anyway, I’m aware of alternate mainframe OSs but I’m not sure how common using one was. Other than OS2, alternate OSs for other systems were rather rare, though it is worth noting that they were not forbidden or blocked.
> 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.
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.
> at major universities and research centres
So not common outside of ivory towers, no?
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.
Before IBM PC computer's weren't particularly commonplace outside of ivory towers either.