Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!burl!ulysses!bellcore!decvax!genrad!panda!talcott!harvard!cmcl2!rna!rocky2!cucard!ccnysci!sukenick From: sukenick@ccnysci.UUCP Newsgroups: net.arch Subject: Re: PDP-8 Message-ID: <239@ccnysci.UUCP> Date: Sun, 9-Mar-86 18:00:34 EST Article-I.D.: ccnysci.239 Posted: Sun Mar 9 18:00:34 1986 Date-Received: Fri, 14-Mar-86 04:17:44 EST References: <187@anwar.UUCP> <1441@gitpyr.UUCP> <890@umn-cs.UUCP> <1468@gitpyr.UUCP> <307@ethz.UUCP> Reply-To: sukenick@ccnysci.UUCP (George ) Organization: City College of New York Lines: 32 >the two "augmented instructions" of the PDP-8. The first of these, >the "IOT" instruction, did I/O operations; the first 3 bits of the >instruction were an octal 6, the next six bits identified the device on >which the operation was to be performed, and the last 3 bits identified the >operation to be performed on the device. > The IOT instruction was also used to set data fields and instruction fields. The PDP8 is a 32K word machine (There might have been a 128k version?) which was divided into 8 fields of 4k each. The addressing modes could access either a page at a time ('direct' addressing - 128 words) or a field ('indirect addressing - 4K words). IOT instructions such as CDF (62X1) (Change Data Field) and CIF (Change Instruction Field) (62X2) changed the field that the instruction using indirect addressing would operate upon. > >Well, I hope the above will also bring back fond memories for other people >who once knew this machine, and will help those who didn't to know a little >more about this very historic machine. > The PDP8 has an interesting peripheral : a 'parallel' processor - the FPP12 floating point processor with its own instruction set, program counter and accumulator. The PDP8 would intialize and start the FPP12. Once started, the CPU and the FPP would operate in parallel, the FPP fetching instructions via DMA. Communication between the two proccesors is either though memory(all of which is shared) or an interrupt that the FPP could set. A nice system for doing real time I/O (via the CPU) and number crunching (FPP) . (If only 32k memory was enough!) (and this was a 1973 machine!) >-------- >"PDP" is a trademark of the Digital Equipment Corporation. >(Incidentally, according to the PDP-8 manual, so is the phrase "Computer >Lab"!)