Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!amdcad!dgcad!dg-rtp!webo!cheshirecat!lewine From: lewine@cheshirecat.webo.dg.com (Donald Lewine) Newsgroups: comp.arch Subject: Re: Low End NeXTs (was Re: Desktop publishing) Message-ID: <1991Apr5.143459.26520@webo.dg.com> Date: 5 Apr 91 14:34:59 GMT References: <34936@athertn.Atherton.COM> <27fa3350.6bc2@petunia.CalPoly.EDU> <1991Apr03.232400.1560@kithrup.COM> <1872@spim.mips.COM> Sender: usenet@webo.dg.com (Usenet Administration) Reply-To: uunet!dg!lewine Organization: Data General Corporation Lines: 38 |> |> >In article <27fa3350.6bc2@petunia.CalPoly.EDU> araftis@polyslo.CalPoly.EDU (Alex Raftis) writes: |> |> >>On the other hand, look at the 68040. It executes instructions at around |> >>1.3 cycles per instuction. |> It is very difficult to verify such a number, or make reasonable |> comparisons without being the architects. As noted in earlier posting, |> if you try to use SPECint/Mhz, you find that the best CISC micros, |> with 128KB external caches, get about .5 - .53 (@ 25MHz), i.e., |> 12.9 - 13.3 for 68040 & 486. RISCs get as much as .75-.80 |> (MIPS, IBM, HP PA). Using that as inverse of CPI, one gets |> cycles/SPEcint of 1.88 (at best) for the CISCs, and 1.25 for RISCs. |> Of course, FP is a more variable story; the RISCs have, at minimum |> at least some additional advantage, more than integer, |> and often a lot more. ERROR: Invalid mixing of Data in line 9! When they say that the 68040 takes 1.3 cycles per instruction, they mean native 68040 instructions. You can not infer anything about clocks per native instruction from a SPECint number. A VAX, a Data General MV/40000, a MIPS R3000 and a 486 all execute a vastly different number of native instructions when running the spec suite. I fully agree with your first statement, "It is very difficult to verify such a number." It is possible to count the instructions executed and the number of clock cycles required, however, it is only easy if you have special hardware and/or simulation tools. The architects tend to have these tools. -------------------------------------------------------------------- Donald A. Lewine (508) 870-9008 Voice Data General Corporation (508) 366-0750 FAX 4400 Computer Drive. MS D112A Westboro, MA 01580 U.S.A. uucp: uunet!dg!lewine Internet: lewine@cheshirecat.webo.dg.com