[pups] re: PDP-9
bqt at update.uu.se
Wed Aug 21 19:21:08 AEST 2002
On Tue, 20 Aug 2002, Dennis Ritchie wrote:
> Bilquist said (quoting Buitinck):
> > 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.
About as I suspected then.
Interesting to hear that the grade of compatibility was that high. I've
neved had the chance to play with any 18-bitters.
> 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.
The Unibus do not require a memory mapped I/O model, though. And it does
have 18 address and data bits. (Two data bits are used for parity on a
The DEC-2020 also used a Unibus.
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at update.uu.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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