Sixth Edition is from 1975. Let's consider its contemporary large-scale multiuser OS environments: * PLATO at UIUC. Much more sophisticated graphics and extensive support for multiuser gaming, but requires custom (and expensive) terminals. Homegrown mainframe, then CDC hardware. * Michigan Terminal System at University of Michigan and elsewhere. Runs on IBM mainframes. * Multics, ITS, TOPS-10, and who knows what else…
Interesting comparisons. Students were definitely using Unix in 1975. My first Unix was actually sixth edition running on a PDP-11/45 at the University of Maryland. I started using it in 1979, but the system had been in use for some years. The system was part of the Computer Vision Lab and was mostly used by grad students for their research. The systems available to the general student population were Univac mainfram…
What I meant was that none of the various large multiuser systems in universities in 1975 ran on Unix. I imagine that most computer people probably vaguely think that Unix was the first large multiuser OS, and that all Berkeley, Stanford, and MIT students were using it, when neither is the case. If a random university student in 1975 wanted a computer account, assuming that such was available to a non-math/engineering/CS student, it would almost certainly have been on a batch system like your UMD example.
As I alluded to at the end, it's striking how within a decade Unix had clearly gained the momentum. Many (even majority) of non-batch systems in 1985 were likely still on VMS, RSTS, TOPS, or some other DEC OS, but those DEC-hardware sites were of course the first to move to Unix despite DEC's best attempts to prevent this.