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From: wunder@wdl1.UUCP
Newsgroups: net.micro
Subject: Re: Ah, yes, the Pdp-7.
Message-ID: <178@wdl1.UUCP>
Date: Sun, 26-Jun-83 20:12:48 EDT
Article-I.D.: wdl1.178
Posted: Sun Jun 26 20:12:48 1983
Date-Received: Tue, 28-Jun-83 01:26:08 EDT
References: sri-arpa.2140
Lines: 32

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

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