Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site sdcsla.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!ittvax!dcdwest!sdcsvax!sdcsla!west From: west@sdcsla.UUCP (Larry West) Newsgroups: net.micro.68k,net.arch Subject: Re: RISC Message-ID: <890@sdcsla.UUCP> Date: Wed, 12-Jun-85 13:34:42 EDT Article-I.D.: sdcsla.890 Posted: Wed Jun 12 13:34:42 1985 Date-Received: Fri, 14-Jun-85 06:08:29 EDT References: <639@vax2.fluke.UUCP> <2743@nsc.UUCP> Reply-To: west@sdcsla.UUCP (Larry West) Organization: UC San Diego: Institute for Cognitive Science Lines: 26 Keywords: RISC, rabbits Xref: watmath net.micro.68k:909 net.arch:1380 Summary: How often do you multiply? In article <2335@cornell.UUCP> hal@gvax.UUCP (Hal Perkins) writes: >In article <601@terak.UUCP> doug@terak.UUCP (Doug Pardee) writes: >>By the way, the Berkeley RISC-II chip has a 330 ns cpu cycle time. The >>10 MHz NS32016 can do a 32-bit register-to-register signed multiply in >>8.3 usec. The RISC-II cpu would have to be able to do the multiply in >>only 25 cpu cycles in order to compete. All the cache in the world >>ain't gonna help... > >Now just a moment... The Berkeley chips were built by academic folks >using conservative design rules, etc. If they had been built by >experienced professional chip designers using state-of-the-art >technology they would have been a lot faster. ... ... Hal's point is valid. Another point to consider is this: what you really want for a general-purpose computer is throughput. How much of a typical instruction stream is composed of 32-bit signed multiply's? Obviously, in many applications, multiplication would take on great significance. But one point of RISC is that optimizing a few special-purpose instructions can hurt you in general-purpose applications. -- Larry West Institute for Cognitive Science (USA+619-)452-6220 UC San Diego (mailcode C-015) [x6220] ARPA: La Jolla, CA 92093 U.S.A. UUCP: {ucbvax,sdcrdcf,decvax,ihnp4}!sdcsvax!sdcsla!west OR ulysses!sdcsla!west