smith@umn-cs.UUCP (06/06/83)
#R:sri-arpa:-109700:umn-cs:6900011:000:241 umn-cs!smith May 4 22:04:00 1983 It is slander to say the PDP-7 (and 1,4,9,15) looked like the PDP-8. I admit that one-address instructions aren't very elegant, and a single AC is a bother, but at least these machines didn't have those god-awful 128 word "pages"... Rick.
Smith@cmu-cs-c@sri-unix.UUCP (06/08/83)
From: David Smith <Smith@cmu-cs-c> It is slander to say the PDP-7 (and 1,4,9,15) looked like the PDP-8. I admit that one-address instructions aren't very elegant, and a single AC is a bother, but at least these machines didn't have those god-awful 128 word "pages"... I think you should use the word "slander" a little more advisedly. When I said the Pdp-7 looked a lot like an 18-bit Pdp-8, I assumed that the perceptive reader would not think I was implying that DEC wasted the extra six bits in the instruction word. Indeed, they raised the "page" size from 128 words to 8192 (while dispensing with the zero/current page bit). They also expanded the opcode from 3 to 4 bits. That afforded them the luxury of instructions for "load accumulator," "execute out-of-line instruction," and "one's complement add" (i.e., with carry out of the high bit being added into the low bit). They still had no subtract instruction. The subroutine jump instruction was the same: store the return address in the first word of the subroutine, start executing at the second. You had to go through the same rigamarole to pick up subroutine parameters. The "operate group" instructions (skip if zero accumulator, etc.) looked the same. The I/O instructions were very similar. The extended arithmetic option added more instructions than the Pdp-8's, but they were of a similar flavor. Either machine's option added a multiplier-quotient register. With either one, you had to store the multiplier or divisor into the instruction stream. Now, I suggest you apologize for your use of the word slander. David Smith
johnl@ima.UUCP (06/14/83)
#R:sri-arpa:-193300:ima:16900007:000:944
ima!johnl Jun 13 11:40:00 1983
It is indeed slander to say that the PDP-7 looked like the PDP-8. The
PDP-7 looked like a PDP-4, the 9 looked like a 7, and the 15 looked like
a 9, with extra bells and whistles being added each time they reimplemented
it.
The PDP-5 was a downsized 4, sort of (12 bits instead of 18) and the 8 was
a reimplementation of the 5, fixing some of the more peculiar warts.
So the 8 looked like the 7, not the other away around.
But actually, we mean "acted" rather than "looked." The 8 physically was
the best looking machine DEC ever built. It had two logic racks over the
front panel, each with an attractive smoked plastic cover covering each
bay. The front panel was real glass, not easily scratched plastic.
We had our PDP-8 mounted on a pallet with handles so we could carry it
around like a sedan chair. There were giants then.
John Levine, decvax!yale-co!jrl, ucbvax!cbosgd!ima!johnl,
{research|alice|allegra|floyd|amd70}!ima!johnlSmith%cmu-cs-c@sri-unix.UUCP (06/14/83)
From: David Smith <Smith@cmu-cs-c>
I think you have a warped sense of what constitutes slander.
The PDP-5 was a downsized 4, sort of (12 bits instead of 18)
and the 8 was a reimplementation of the 5, fixing some of the
more peculiar warts. So the 8 looked like the 7, not the
other away around.
If you agree that the 8 looked like the 7, I feel vindicated.
Since the Pdp-8 series was much more widely sold than the 4/7/9/15,
and more people were acquainted with it, I felt it made sense to
describe the 7 in terms of its similarities to the 8.
"What does your father look like?" "He looks like me."
Does that imply I preceded my father?
But actually, we mean "acted" rather than "looked."
Nah. I meant "looked." The appearance of the instruction formats.
We had our PDP-8 mounted on a pallet with handles so we could carry it
around like a sedan chair. There were giants then.
John Levine, decvax!yale-co!jrl, ucbvax!cbosgd!ima!johnl,
{research|alice|allegra|floyd|amd70}!ima!johnlwunder@wdl1.UUCP (06/27/83)
We shouldn't stop this history of the PDP-7 just when it was getting fun! The PDP-4 was a fairly straightforward redesign of the PDP-1, and shared most of its instruction set. The 4 used twos-complement, rather than ones-complement, arithmetic and introduced the famous JSR used in all the later machines. The precursor of the PDP-1 was the TX-0, designed by Ken Olsen and J. L. Mitchell at MIT. The instruction set probably sounds familiar: "The initial version of the TX-0 had only four instructions encoded in two bits, leaving sixteen bits to address the large, 64-Kword memory. Three of the instructions accessed memory: "store in location", "add from location", and "transfer if Accumulator is negative to location". The fourth instruction, "operate", was for program controlled I/O transfers and included commands that could be combined to produce a large number of instructions. This combining process was called "microprogramming" ... " The above quote is from "The PDP-1 and Other 18-Bit Computers" by C. Gordon Bell, Gerald Butler, Robert Gray, John E. McNamara, Donald Vonada, and Ronald Wilson (Whew!). That is a chapter in the book "Computer Engineering: A DEC View of Hardware Systems Design", by Bell, Mudge, and McNamara published by Digital Press. They really do write "64-Kword", in case you thought that that was a typo. The Kword is an old DEC unit of measure, common on price lists (take that, spelling police!). wunderwood UUCP: fortune!wdl1!wunder ARPA: wunder@FORD-WDL1 Phone: (415) 852-4769
hoffman@pitt.UUCP (06/29/83)
With all of this discussion of the PDP-7 and its kin, I just had to add that we still have a PDP-4. Since there were only 45 of these ever built, I wonder how many more are still around. Ours is a PDP-4B, s/n 32. It has a paper tape reader/punch, crt display with light pen, DECtapes, and a TTY28 console. Internally, it has 4K 18-bit words of core memory, an extended arithmetic element (mul, div, shift), and an A/D converter. The PDP-4 does, by the way, have *both* one's complement (ADD) and two's complement (TAD) arithmetic. It plays a mean game of Space War... ---Bob (Don't throw that old computer out!) Hoffman pitt!hoffman, hoffman.pitt@Udel-Relay [Founding member of The Computer Museum]
bhaskar@fluke.UUCP (07/07/83)
Has anyone else out there used a PDP-1? The PDP-7 sounds very much
like a direct descendant of the 1. I fondly remember a PDP-1D (there
were only two built, #s 45 and 48, I believe, and when Stanford junked
theirs we got it at the Indian Institute of Technology, Kanpur). It
had 32K of 18-bit words in 4K pages, but Stanford had modified it to
add an index register and other goodies. Consequently, one of the
instructions was FFI -- Fiddle Following Instruction (sic) which did
what you think it did because only 5 bits were reserved for the
opcode! And, yes, it played a mean game of Space War (I understand the
original was written for the other PDP-1D at MIT by McCarthy or Minsky
-- can anyone corroborate?). When there was a program bug, we checked
the hardware along with the software... Are there any IIT/K people on
the net who were there more recently than 1975 and who know what
happened to it?
K.S. Bhaskar {allegra,lbl-csam,microsoft,sb1,uw-beaver}!fluke!bhaskarmark@umcp-cs.UUCP (07/10/83)
Sure, I've used a PDP-1, only about 10 years ago. The things I
remember best are
(a) the clock speed knob on the front panel.
(b) the assembler which punched out your program onto paper tape
backwards so when the loader read it the relocation information
was at the front.
Neither Minsky nor McCarthy wrote the first spacewar, but it was
Minsky's lab at MIT where the writing was done. Minsky now says
proudly that he wants his lab to remembered as the first to
ban game playing during the day.
--
spoken: mark weiser
UUCP: {seismo,allegra,brl-bmd}!umcp-cs!mark
CSNet: mark@umcp-cs
ARPA: mark.umcp-cs@UDel-Relayjim@grkermit.UUCP (07/11/83)
That pdp-1 you spoke of is currently at the Digital Computer Museum
in Marlboro, MA. It still runs spacewar, when they do fire it up for big
tour groups. For anyone not familiar with this museum that will be in the
New England area, I highly recommend their exhibits, from early
"tinker-toy" computers to water-cooled mainframes...
--
Jim Morton GenRad Inc., Concord, Mass. {...decvax!genrad!grkermit!jim}smh@mit-eddie.UUCP (Steven M. Haflich) (07/25/83)
Re the highly-recommended DEC Museum in Marlborough MA., I have recently heard that DEC will be moving same (next summer?) to a far more accessible location in Boston, near the Aquarium. Steve Haflich genrad!mit-eddie!smh