[pups] Re: PDP-9

[pups] Re: PDP-9

[Roger Ivie]

Dennis Ritchie said:
> 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.

According to Gordon Bell's "Computer Engineering", the primary differences
from the -4 to the -7 were switching from 6-bit to ASCII I/O devices and
the addition of a trap mechanism. The -9 primarily changed the memory
system, going to 2-1/2D core; it was also microcoded. The -15 went to
TTL ICs and added index registers and memory relocation. He says
"The PDP-9 instruction compatibility was acheived with three minor
exceptions about which no complaints were received", although I don't
see an explanation of the exceptions.

http://research.microsoft.com/users/GBell/Computer_Engineering/

-- 
Roger Ivie
ivie at cc.usu.edu

[pups] re: PDP-9

[Frank Wortner]

on 8/21/02 5:21 AM, Johnny Billquist at bqt at update.uu.se wrote:

> 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.

You can indulge in 18-bit nostalgia courtesy of Bob Supnik.  His Computer
History Simulation Project includes simulators for the DEC 18-bit computer
line.  Check out http://simh.trailing-edge.com/ if you are interested.

Unfortunately,  there isn't much surviving software for these machines.  The
site does include a PDP-7 based simulator of the PDP-8(!),  and the
"Advanced Software System" OS for the PDP-15 (which I believe will also run
on the PDP-9).

Bob's wish list includes a plea for DECsys and the First through Fourth
Editions of Unix,  but unless someone unearths a cache somewhere,  these may
be lost to history.  Too bad. :-(

-- 
Frank

"It's snowing still.  *And* freezing.  However,  we haven't had an
earthquake recently."
* Eeyore,  "The House at Pooh Corner"

[pups] re: PDP-9

[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

[pups] re: PDP-9

[Johnny Billquist]

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
PDP-11.)
The DEC-2020 also used a Unibus.

	Johnny

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

[pups] re: PDP-9

[Lars Brinkhoff]

Dennis Ritchie <dmr at plan9.bell-labs.com> writes:
> The 7, 9, 15 were very compatible.  [...]  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.

No attempts to run on a PDP-4, then?

-- 
Lars Brinkhoff          http://lars.nocrew.org/     Linux, GCC, PDP-10,
Brinkhoff Consulting    http://www.brinkhoff.se/    HTTP programming

[pups] re: PDP-9

[Dennis Ritchie]

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.

Both of the machines we tried were being used by other groups
and we couldn't squat on them as with the PDP-7.
I recall that  the -15's main job was controlling a
step-and-repeat camera that exposed LSI masks.

	Dennis