Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!wivax!decvax!harpo!seismo!hao!hplabs!hpda!fortune!wdl1!wunder 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 UUCP: fortune!wdl1!wunder ARPA: wunder@FORD-WDL1 Phone: (415) 852-4769