From: kcwellsc@watdragon.uwaterloo.ca (Ken Wellsch)
Subject: Re: UNIX Operating System
Organization: University of Waterloo
Date: Sun, 15 Nov 1992 19:17:53 GMT

According to "The UNIX Time-Sharing System" paper (I'm looking at a copy
from "UNIX Programmer's Manual - Vol 2" from Bell Labs), there have been
(as of V7 UNIX, 1978) four versions of UNIX:

	(1) circa 1969/70 running on PDP-7 and PDP-9's
	(2) circa 1971/72 running on a PDP-11/20
	    (Dennis Richie creates C, the O/S is rewritten 1973)
	(3) circa 1974/75 running on PDP-11/40,45 (called V6)
	(4) circa 1978 running on PDP-11/70 (called V7)

Version 6 UNIX was in fact distributed according to it's documentation
on three RK05's or 9-track tape.  Versions like "VENIX" I claim are
actually derived from V6 (I use the filesystem as the major clue) and
would thus run on the smaller address machines like the 11/40 (max 64Kb
process size).

Many people have seen true V7 shoe-horned onto a small address machine
(e.g. 11/23) but as Steven said it is not a pretty sight.  I recall
a process limit possibly in the single digit range (for the whole system).

UNIX was a research O/S (and I feel still is 8-) and the designers
adapted to new hardware as it came out.  Shifting to the larger
process space (split I&D) machines was not at all surprising (take
a look at how full your disks are and the old full+10% always seems
to come true regardless of how much new mem/disk you buy).

My feeling is the Berkeley folks early on when doing the 2bsd version
wanted to counter the split-I&D aspect and developed the large instruction
space model that allowed an enhanced V7 kernel to fit on a nonsplit
machine.

Of course AT&T licensing applies to all this software and as it costs
lots of money (I recall $150,000 for a SysV source commercial license)
the people who could afford it (commercial interests) went for the
current and future hardware where the money can be made.
(it would take such a commercial interest to also afford a binary
resale license in order to even sell a copy they would have to
develop for the PDP-11 - the cost isn't worth it to them I suspect)

There is no denying that with a lot of effort, much software can be reduced
dramatically in size requirements, but the people who can "legally" play
with source don't need to fit things as small as 64Kb or 128Kb any more
and the hobby people can't legally afford the licensing...

It is almost ironic that of the three points the paper (referenced earlier)
mention as "design influences", one of them is:

  "... there have always been fairly severe size constraints on the
  system and its software.  Given the partially antagonistic desires
  for reasonable efficiency and expressive power, the size constraint
  has encouraged not only economy, but also a certain elegance of
  design. This may be a thinly disguised version of the ``salvation
  through suffering'' philosophy, but in our case it worked."

But with all honesty, at some point it becomes practically impossible
to have as severe a size constraint as a PDP-11 now represents in
light of current hardware technology (obviously depending on application,
there is still a lot of PDP-11 use today using DEC OS's)