From mboxrd@z Thu Jan  1 00:00:00 1970
From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Date: Wed, 25 Apr 2018 18:55:51 -0400 (EDT)
Subject: [TUHS] /dev/drum
Message-ID: <20180425225551.3685318C086@mercury.lcs.mit.edu>

    > 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