[pups] re: PDP-9
cdl at mpl.ucsd.edu
Thu Aug 22 05:59:42 AEST 2002
> To: pups at minnie.tuhs.org
> From: Dennis Ritchie <dmr at plan9.bell-labs.com>
> Subject: [pups] re: PDP-9
> Date: Tue, 20 Aug 2002 23:55:55 -0400
> Bilquist said (quoting Buitinck):
> > > 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.
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 lowenstein marine physical lab u.c. san diego
clowenst at ucsd.edu
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