[pups] re: PDP-9

[cdl@mpl.ucsd.edu (Carl Lowenstein)]

> 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.
> 
> 	Dennis

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 at ucsd.edu