26 Apr
2018
26 Apr
'18
4:55 a.m.
From: Johnny Billquist
PDP-11 have 8K pages.
Segments. :-) (This is an old argument between Johnny and me, I'm not trying
to re-open it, just yanking his chain... :-)
On a PDP-11, all your virtual memory was always there
when the process
was on the CPU
In theory, at least (I don't know of an OS that made use of this), didn't the
memory management hardware allow the possibility to do demand-paging? I note
that Access Control Field value 0 is "non-resident".
Unix kinda-sorta used this stuff, to automatically extend the stack when the
user ran off the end of it (causing a trap).
you normally did not have demand paging, since that
was not really
gaining you much on a PDP-11
Especially on the later machines, with more than 256KB of hardware main
memory. Maybe it might have been useful on the earlier ones (e.g. the -11/45).
Noel