[TUHS] Split addressing (I/D) space (inspired by the death of the python... thread)

[Noel Chiappa]

    > From: Will Senn

    > Does unix (v7) know about the PDP-11 45's split I/D space through
    > configuration or is it convention and programmer's responsibility to
    > know and manage what's actually available?

There are two different cases: i) support of split I+D in the kernel, and
ii) support of split I+D in  user processes. Both arrived with V6; the
V5 source:

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

(former for kernel; later for users) shows no sign of it.


    > From: Kenneth Goodwin <kennethgoodwin56 at gmail.com>

    > 1.  I don't think the 11/45 had split I & d.
    > But I could be wrong.
    > That did not appear until the 11/70

You are wrong.

The chief differences between the KB11-A&-D of the -11/45 and the -B&-C of
the -11/70 were i) the latter had a cache, and ii) the latter used the 32-bit
wide Main Memory Bus, which also allowed up to 4 Mbytes of main memory.
Detail here:

  https://gunkies.org/wiki/PDP-11/70

along with a couple of lesser differences.


    > From: "Ronald Natalie"

    > with only 8 segment registers combined for code, data, and stack

I think you meant for code, data, and user block.

    > The 55 (just a tweaked 45)

The /50 and /55 had the identical KB11-A&-D of the /45; the difference was
that they came pre-configured with Fastbus memory.

    > In addition the 23/24/J-11 and those derived processors did.

No; the F-11 processors did not support I&D, the J-11 did.


	Noel