Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!lamaster From: lamaster@ames.arc.nasa.gov (Hugh LaMaster) Newsgroups: comp.arch Subject: Re: Longer load/store because of register windows Message-ID: <17284@ames.arc.nasa.gov> Date: 28 Oct 88 23:02:38 GMT References: <156@gloom.UUCP> <310@lynx.zyx.SE> <332@pvab.UUCP> <15964@agate.BERKELEY.EDU> <23367@amdcad.AMD.COM> <16003@agate.BERKELEY.EDU> <469@oracle.UUCP> <7041@winchester.mips.COM> <17268@shemp.CS.UCLA.EDU> <7195@winchester.mips.COM> Reply-To: lamaster@ames.arc.nasa.gov.UUCP (Hugh LaMaster) Organization: NASA Ames Research Center, Moffett Field, Calif. Lines: 31 In article <7195@winchester.mips.COM> mash@winchester.UUCP (John Mashey) writes: >In article <17268@shemp.CS.UCLA.EDU> marc@cs.ucla.edu (Marc Tremblay) writes: > >>Having a multiple-window register file, or more precisely, having many >>registers, slows down the processor cycle. Even with an independent port for >Could you quantify the hit from these issues, or point at some references >that show data for this? I don't know enough of the details to know why this is so, but I have been told that "all other things being equal" (i.e. a typical processor design with typical technology) that it is difficult to provide more than about 32 registers with single cycle read/write access. The only machine that I know well that is germane is the Cyber 205, which has 256 G.P. registers and takes two cycles to read/write the register file, and which has additional logic to hide that fact in most circumstances. So, it doesn't prove the case, but it doesn't contradict it either. Since 32 is usually acknowledged to be in the diminishing returns area, I'm not sure how many people have tried to provide more registers. I have no knowledge of how the registers are organized in one of the new register window machines, and whether this is a problem on those machines. Anyway, the original poster's hypothesis, that "many" registers creates an access speed problem, seems reasonable at this point. -- Hugh LaMaster, m/s 233-9, UUCP ames!lamaster NASA Ames Research Center ARPA lamaster@ames.arc.nasa.gov Moffett Field, CA 94035 Phone: (415)694-6117