Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!apple!mips!redwood.mips.com From: wje@redwood.mips.com (William J. Earl) Newsgroups: comp.arch Subject: Re: machines with some loadable microcode are easier to fix Keywords: microcode hardware bugs Message-ID: <44558@mips.mips.COM> Date: 7 Jan 91 07:23:30 GMT References: <71537@bu.edu.bu.edu> <1991Jan04.035359.12547@kithrup.COM> <777@TALOS.UUCP> <1991Jan04.205635.16420@iecc.cambridge.ma.us> Sender: news@mips.COM Reply-To: wje@redwood.mips.com (William J. Earl) Organization: MIPS Computer Systems Inc. Lines: 33 In-reply-to: johnl@iecc.cambridge.ma.us (John R. Levine) In article <1991Jan04.205635.16420@iecc.cambridge.ma.us>, johnl@iecc (John R. Levine) writes: > In article <777@TALOS.UUCP> jerry@TALOS.UUCP (Jerry Gitomer) writes: > >Given these circumstances the solution was to use loadable microcode to > >make a group of dissimilar computers look alike to the programmer. The > >best illustration was the IBM 360 family. To the programmer each 360 was > >a 32-bit word machine with 16 registers. The 360/30 was an 8-bit machine, > >the 360/40 was a 16-bit machine, the 360/50 was the only 32-bit machine in > >the family, the 360/65 was a 64-bit(?) machine, and the 360/75 was even > >bigger. >... > The model 20 was a strange case, it was a desk-sized machine whose > architecture was an almost compatible subset of the larger machines although > the I/O was entirely different. The slower models had ROM microprograms, but > the submodel 5, the fastest one, stored the microcode in the same core memory > as the application code. If the microcode got frotzed, (core survives > power-off, so that was infrequent) there was a large deck of cards in the > back from which you could reload the microcode. I know people who hacked in > extra instructions, but it was certainly not sanctioned by IBM. Since I/O > was heavily assisted by the microcode, e.g. there was a single "read card and > translate to EBCDIC" instruction, they may have distributed extra microcode > to go with optional peripherals. The 20 was a bit more than "desk-sized." It was more like "Xerox 7000 series copier-sized," and it was not really compatible, in that it would not run any non-trivial S/360 program. At the site where I encountered it, it made a nice RJE batch station, with card reader, card punch, and line printer. -- William J. Earl wje@mips.com MIPS Computer Systems 408-524-8172 930 Arques Avenue, M/S 1-03 FAX 408-524-8401 Sunnyvale, CA 94086-3650