[...], I suspect some would want to use the floating-CSR rules
simply bceause they were The Way It Was Done Back Then.
That's precisely the mindset at the museum, with DEC and other
systems.
Which is kindof weird, because pretty much noone, nowhere, that I
know of, did it that way back then. [...] just grabbed any free CSR
address range [...]
That's what I would expect in an installation full of people who
understand Unibus addressing and the like.
It would not surprise me, though, if there were sites at places like
banks that had nobody on staff who understood anything and called their
four-hour-response field-service number whenever _anything_ went wrong.
It wouldn't surprise me if some such sites used floating-CSR rules not
because it produced a better system but simply because it was what DEC
officially recommended. (Which it was, wasn't it?)
The only site I had anything to do with that was running a DEC OS on
Unibus/Qbus hardware was in academia, full of computer geeks. We had a
device whose interface was multiple Unibus-form-factor cards that
required a custom-wired section of Unibus backplane, with a custom
driver for it. The sort of place that used the term "field circus" and
told jokes like "How do you tell a DEC field service tech with a flat
tire? He's the one swapping tires to see which one is flat. How do
you tell a DEC field service tech who's out of gas? He's the one
swapping tires to see which one is flat." (This was back in the '80s,
when a field service tech who wasn't "he" was basically unheard of.)
We too did the just "grab a free range" sort of thing.
I never had any significant contact with the non-geeky sites; I have no
personal experience of what they did. Does your experience include any
such? In particular, does your "noone...did it that way" remark apply
to them too? (I'm not challenging, just curious. As I say, I have no
experience either way on the question myself. But I would find it
mildly surprising if DEC had maintained these elaborate rules even
though nobody was paying any attention.)