[TUHS] Can PDP-11/23 PLUS run Unix?

[Noel Chiappa via TUHS]

    > From: Phil Budne

    > V7M has overlays

Ah, the CHWiki doesn't have a page for that system; I'll have to add it.

Yes, it does seem to have had _kernel_ overlays before 2.9 (I looked, to see
if I could find any direct credit in 2.9, to indicate that their support for
kernel overlays came from V7M, but couldn't; I'm too lazy to do sources
compares).

I say "_kernel_ overlays" because I gather (see some evidence, below) that
use-of/support-for overlays in _processes_, in user mode, preceded
use-of/support-for overlays in the kernel.

See:

  "Running Large Text Processes on Small Unix Systems", Charles Haley,
  William Joy, William F. Jolitz
  https://www.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/doc/ovpap

  "We describe a set of simple modifications to the Unix system, which permit
  larger programs to be run than has previously been possible. In particular,
  the 'f77' and 'a68' compilers and version 2 of the 'ex' editor, which
  previously would not run on the non-separate I/D machines such as the
  11/23, 11/34 and 11/40, may be run, without source code modification, using
  this scheme. This scheme will also allow processes larger than 65K bytes of
  instruction space to run on all 11/ cpu's with segmentation hardware.

and:

  "How to use the UNIX Automatic Text Overlays: A Tutorial", Barbara Bekins,
  Bill Jolitz
  https://www.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/doc/ovtutorial

The former unfortunately does not have a date on it; the latter has a date of
10/20/81, but we can infer that the original work was before that. It does
appear to be later than "The Second BSD" (1979-04); there's nothing about
overlats that I could find there..


V7M contains notes that more or less state that its use-of/support-for
overlays in the kernel is based on the prior support for overlays in
_processes_, done at Berkeley:

  This directory contains the C overlay loader and some other junk. ... Covld
  is derived from Bill Joy's covld .. The paper in ovpap.n describes the
  original Berkeley overlayed text scheme which was intended for use in user
  mode programs. I use overlays only for the kernel itself.

  https://www.tuhs.org/cgi-bin/utree.pl?file=V7M/src/cmd/covld/README


I also have a memory that someone did some work that allowed large amounts of
disk buffers (and maybe clists too), which were not statically mapped into
kernel address space; one segment was used to map them in, as needed.

Can anyone point me at anything which covers that? (URL's would be a big plus!)
I will add all that (and this) to the appropriate places in the CHWiki.


I understand that all these kludges were not really important; in the long run,
they were dead ends. I just want to see them all documented, and credit
correctly assigned (as above, for the code overlays).

	Noel