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Date: Wednesday, 20 August 1986 03:42-EDT
From: Mark Crispin <MRC%PANDA@SUMEX-AIM.ARPA>
To: TOPS-20@SU-SCORE.ARPA, Boken@RED.RUTGERS.EDU
Re: DEC's PDP's
Postal-Address: 1802 Hackett Ave.; Mountain View, CA 94043-4431
Phone: +1 (415) 968-1052
A number of people have requested my list of all the DEC PDP's,
so I thought I'd bore you all with it.
The PDP-1 was an 18 bit machine. It was DEC's first computer,
and some of the first timesharing systems were designed for it. It's
also unique in being one's complement; all later DEC computers were
two's complement. Some machines, such as one of MIT's PDP-1s, were in
operation until the late '70s.
The PDP-2 was a designation reserved for a 24 bit machine, but as
far as I can tell it was never even designed and definitely none were
ever built.
The PDP-3 was a 36 bit machine that was designed but never built
by DEC. However, Scientific Engineering Institute built one in 1960.
The PDP-4 was an 18 bit machine that was intended to be a
cheaper, slower alternative to the PDP-1. It was so slow that it
didn't sell well, although it was interesting for its
auto-incrementing memory registers. It was not program-compatible
with the PDP-1, but its instruction set was the basis of DEC's future
18 bit computers.
The PDP-5 was a 12 bit machine designed to be a small laboratory
system. It used many of the ideas in the LINC (Laboratory Instruction
Computer, designed by Lincoln Labs at MIT, some of which were built by
DEC).
The PDP-6 was a 36 bit machine and the first machine to implement
the most wonderful computer architecture known to man. It was rather
expensive and difficult to maintain, and not many were sold. As a
result, DEC cancelled 36 bit computers for what was to be the first of
many times.
The PDP-7 was an 18 bit machine and the sucessor to the PDP-4.
It was a major price/performance win over the PDP-4 and the first DEC
computer to use wire-wrapping.
The PDP-8 was a 12 bit machine and the sucessor to the PDP-8. It
basically defined the term "minicomputer", and went through several
incarnations. The original PDP-8 was followed by the extremely slow
PDP-8/S (as bad as the PDP-4 was to the PDP-1, but at least the /S was
program-compatible). DEC recouped with the PDP-8/I (using MSI
integrated circuits) and the smaller PDP-8/L, and somewhat later came
out with the "Omnibus 8" machines -- the PDP-8/E, the PDP-8/F (a
half-sized version of the PDP-8/E), the PDP-8/M (an OEM version of the
PDP-8/F), and the final machine, the single board PDP-8/A. The
PDP-8/A still exists after a fashion as a current DEC product.
The PDP-9 was an 18 bit machine and the sucessor to the PDP-7.
It had a faster memory than the PDP-7 and was the first
microprogrammed DEC computer. Modulo a 300 wire(!) ECO required in
the first machines, the PDP-9 was a reliable machine and some are
still in operation today. There was a short-lived PDP-9/L.
The PDP-10 was a 36 bit machine and the sucessor to the PDP-6.
It is especially noted for its software, which represents the pinnacle
of DEC software engineering and has never been equalled. The first
KA10, largely installed in universities, created a whole generation of
timesharing hackers. The follow-on KI10, with paging and using IC's
instead of discrete components but otherwise unexciting, mostly was
sold to commercial organizations. The KL10 went through several
incarnations and is today the most representative of this marvelous
machine. The KS10 was a small, low-speed (approximately KA10
performance) processor which was DEC's last successful implementation
of this architecture.
The PDP-11 was a 16-bit machine that went through more
implementations and operating systems than can be counted. Presently
it superceded the less powerful PDP-8 as the representative
minicomputer. While the PDP-11 used octal, it was in its deep heart
of hearts a hexidecimal machine, and the first indicator of the
creeping IBMification of DEC that took full fruit in the VAX. [I can
hear the flames now...] Rather than fight it the customers loved it;
more PDP-11's have been sold than any other DEC computer (possibly
more than all the others combined).
The PDP-12 was a 12 bit machine and the sucessor to the PDP-8.
It combined a LINC and a PDP-8 type processor in the same box and
basically was a new model of the LINC-8 which was the same thing.
No PDP-13 was ever designed or built. Even DEC gets
superstitious.
The PDP-14 was a 12 bit machine with a 1 bit register. It was
used as a process control engine in applications that were felt to be
too rugged for a PDP-8, and basically replaced a set of relays. Later
DEC made PDP-8's suitable for this sort of thing, but it didn't stop
them from the ultimate silliness of building a PDP-14 that used a
PDP-8 as its console processor!
The PDP-15 was an 18 bit machine and the final one of this design
built by DEC. More PDP-15's were built and sold than any of the
others, and it went through several incarnations including some which
used a PDP-11 as a front end. Apparently the cancellation of the
PDP-15 came as a great surprise to the "Tiger Team" who worked on it,
although considering its general ungainliness compared to comparable
performance PDP-11's it wasn't surprising. In many ways the PDP-15
died for the same reason the PDP-10 did.
The PDP-16 was a "roll your own" 16 bit machine based on various
"building blocks". Every PDP-16 was essentially custom-designed by
the customer. It got a fair amount of attention when it was announced
but evidentally didn't sell very well.
There was no PDP-17 or any other designator. DEC apparently
decided that "PDP" had a perjorative ring to it.