Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!wuarchive!uunet!mcsun!ukc!dcl-cs!aber-cs!athene!pcg From: pcg@cs.aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.arch Subject: Re: R4000 Message-ID: Date: 13 Feb 91 20:12:37 GMT References: <45448@mips.mips.COM> <1991Feb12.203337@pbird14.prime.com> Sender: pcg@aber-cs.UUCP Organization: Coleg Prifysgol Cymru Lines: 50 Nntp-Posting-Host: odin In-reply-to: danw@pbird14.prime.com's message of 13 Feb 91 01:33:37 GMT On 13 Feb 91 01:33:37 GMT, danw@pbird14.prime.com (Dan Westerberg) said: danw> I mean, so the R4000 uses an 8 stage pipe, so what? [ ... ] I danw> mean, c'mon, aren't pipelines old hat? Very old indeed. In fact I doubt very much that the R4000 pipeline, in both its 8 stage and issue rate being double the external clock aspects, is new. Rumour has it that the ill-fated Z80,000 had a very long pipeline and used similar tricks. In any case long pipelines have big problems. Average interjump distance is often quite a bit smaller than 8 instructions. It is longer than that in very straight numerical codes. Long pipelines are poor man's vector processors, tailored for FIFO access patterns. Non numerical codes normally benefit a bit more from superscalar than from long pipelines, whether their issue rate is twice the external clock or not. My usual reference, Ibbett&Morris "The MU5 computer system", MacMillan, comes in handy when thinking about long pipelines. danw> What I find rather impressive is a 64-bit single-cycle integer danw> ALU! Doing a full 64-bit operation in only 10ns (100MHz) in CMOS danw> is one hell of a feat! Agreed... As a final unrelated note: I don't find the R4000 architecture announcement premature, and I don't think that MIPS can be compared in any way to IBM as to ambitions to freeze their competitor's market. I think that they should have published more details and in a neutral scientific journal, say SIGARCH. As things stands, they have done press releases over something fuzzy. Seems designed to whet the appetite without committing oneself too much. Well, if the intention was to give a statement of direction, a more detailed paper in SIGARCH would have given it, and everybody would have understood that it was not about product announcements. All in all I find the fuzzy press release a very venial sin. Admirable restraint, compared to some much more trumpeted vapourware we have seen before. -- Piercarlo Grandi | ARPA: pcg%uk.ac.aber.cs@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcsun!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk