21 Aug
2002
21 Aug
'02
9:59 p.m.
To: pups(a)minnie.tuhs.org
From: Dennis Ritchie <dmr(a)plan9.bell-labs.com>
Subject: [pups] re: PDP-9
Date: Tue, 20 Aug 2002 23:55:55 -0400
Bilquist said (quoting Buitinck):
What I remember, as the last gasp of PDP-15 production was a
dual-processor setup, linked with a PDP-11. The intent was to take
advantage of the lower-cost Unibus peripherals. I remember the
sales literature, but do not recall ever seeing one.
carl
--
carl lowenstein marine physical lab u.c. san diego
clowenst(a)ucsd.edu
> we all know that UNIX first ran on the PDP-7
and then on the PDP-11/20,
> but does anyone know anything about PDP-9 UNIX? it\'s mentioned in \"The
> UNIX Time-Sharing System\" in the V7 manual:
>
> \"The earliest [version of UNIX] (circa 1969-70) ran on the Digital
> Equipment Corporation PDP-7 and -9 computers.\"
Hmmm, I cannot exactly answer that, but the PDP-7
and PDP-9 were both
18-bit machines, and somewhat compatible, I believe.
The whole line is (I believe):
PDP-4 -> PDP-7 -> PDP-9 -> PDP-15
So I guess that if you had it running on a PDP-7,
you could probably
almost take the code unmodified and run it on the PDP-9.
The PDP-15 have a different bus (Unibus?) I believe, and thus,
peripherials are different from the predecessors.
This obviosuly affects the OS. :-)
The 7, 9, 15 were very compatible. I think the -15
had some scheme for using an index register, which
the earlier ones didn't have, but it was otherwise
pretty much identical in IS architecture.
There was very little rewriting to try Unix out
on the -9 and -15; perhaps just some tweaks in
the disk device commands. I don't think the
system actually ran on either for more than a few
hours. Ken was just playing around.
The -15 may have had an electrically different
bus, but I'm reasonably sure it was not a Unibus.
All of them used IOT instructions, not memory-mapped
IO registers.
Dennis