[TUHS] Unix & Memory Management Units (MMU)

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Dec 8 06:12:03 AEST 2016


    > From: Clem Cole

    > DEC's Custom Special Systems (CSS) group .. build a simple base/limi
    > register device, soon after the 11/20 was released.> ... So an early
    > version of after the original 11/20 port from the PDP-7 had this
    > however.....

Oh, right, I'd forgotten about that: the KS-11 - I've previously enquired to
see if anyone had _any_ documentation for this, but so far, nada.

    > I would look at Warren's First Edition work to see if there were dregs
    > of this in that code base

Alas, I'd already had that idea (to try and at least re-create a programming
spec, at least, for the KS11). There do not seem to be any traces there,
perhaps because that code came from a document entitled "Preliminary Release
of Unix Implementation", which argues that it's a very early 'version' of V0
(the early 'versions' weren't very formal, there was a continuous process of
change/improvement going on, apparently).


    > It is also noted that the 45 class system (45/55/70/44) had "17th"
    > address bit - i.e.  split I/D space.  I believe that this is when "magic
    > numbers" were really introduced so that could be supported.

No, they came in first for 'pure text' (0410):

  http://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/nsys/ken/sys1.c

which I would expect arrived to minimize swapping on machines with small
amounts of real memmory.

Support for user split-I/D (411) didn't arrive until Version 6:

  http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/sys/ken/sys1.c

although IIRC split I/D in the kernel was supported supported slightly
before it was in user - although V5 didn't:

  http://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/sys/conf/mch.s

so it couldn't have been much earlier than V6.

	 Noel


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