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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.cs.su.oz.au!inferno.mpx.com.au!goliath.apana.org.au!news.syd.connect.com.au!news.mel.connect.com.au!munnari.OZ.AU!news.ecn.uoknor.edu!news.eng.convex.com!newshost.convex.com!cs.utexas.edu!geraldo.cc.utexas.edu!usenet From: ccheney@mail.utexas.edu (Chris Cheney) Newsgroups: comp.unix.bsd.freebsd.misc,alt.comp.periphs.mainboard.asus,comp.sys.ibm.pc.hardware.systems,comp.os.linux.hardware,comp.sys.intel Subject: Re: PCI bus freq with CPU freq at (X * 40)Mhz? Date: Mon, 04 Mar 1996 20:07:59 GMT Organization: The University of Texas at Austin, Austin, Texas Lines: 27 Message-ID: <4hfipf$n74@geraldo.cc.utexas.edu> References: <DnpJqF.82n@info.elvisti.kiev.ua> NNTP-Posting-Host: slip-41-2.ots.utexas.edu X-Newsreader: Forte Free Agent 1.0.82 Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:14777 alt.comp.periphs.mainboard.asus:11707 comp.sys.ibm.pc.hardware.systems:28377 comp.os.linux.hardware:32025 comp.sys.intel:66319 stesin@elvisti.kiev.ua (Andrew V. Stesin) wrote: >Sorry for ignorance, but what will be the frequency on a PC's PCI bus >when the CPU runs at main frequency of 40MHz (DX2/80, DX4/120 i.e.)? >I always thought that PCI will than run at 40MHz too. >But was told today that it will be only 20MHz?! Oh God. >How can I check this for sure, without running hated benchmarks, >but only by exploration of MB jumpers? >I was also told that having 40MHz will probably cause >an addition of extra wait states for cache and RAM access, >thus making a box considerably _slower_ for real work >than with 33MHz CPU main frequency, especially for UNIX-like OS >(FreeBSD in my case, but who cares). Any comments on this one? >And, in case both statements are true, why bother looking >at (X * 40)MHz 486 CPUs at all? The PCI commonly used specification goes from 25 Mhz to 33 Mhz. I think I have heard that it is possible to go to 66 Mhz, but I think most peripherals are only up to the 33 Mhz spec so pushing them to 40 Mhz sometimes causes problems. Chris