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Newsgroups: comp.unix.bsd.freebsd.misc,alt.comp.periphs.mainboard.asus,comp.sys.ibm.pc.hardware.systems,comp.os.linux.hardware,comp.sys.intel Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!newshost.telstra.net!act.news.telstra.net!psgrain!newsfeed.internetmci.com!in2.uu.net!news.new-york.net!ritz.mordor.com!ritz From: ritz@ritz.mordor.com (Chris Mauritz) Subject: Re: PCI bus freq with CPU freq at (X * 40)Mhz? X-Newsreader: TIN [UNIX 1.3 950824BETA PL0] Lines: 78 Organization: Mordor International Message-ID: <Dns7BK.DBI@ritz.mordor.com> References: <DnpJqF.82n@info.elvisti.kiev.ua> <4hg8sa$1jn@heist.demon.co.uk> Date: Tue, 5 Mar 1996 06:28:32 GMT Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:14864 alt.comp.periphs.mainboard.asus:11906 comp.sys.ibm.pc.hardware.systems:28508 comp.os.linux.hardware:32185 comp.sys.intel:66491 Iain Baird (iain@heist.demon.co.uk) wrote: : Andrew V. Stesin (stesin@elvisti.kiev.ua) 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? : : PCI is specified to run at up to 33MHz. To accomodate faster CPU : clocks motherboards can provide the facility for PCI to run at : some fraction of the CPU. My motherboard (GA-486AMS) allows a : CPU:PCI ratio of 1:1 or 2:1, configured in the BIOS setup. In : principle other ratios could be used (e.g. 4:3), but I'm not aware : of any motherboards which support this. : : Having said that, I have run PCI at 40MHz with a DX4-120, and it : worked (with AHA-2940 and S3-968). This made little or no difference : to kernel build times compared to 20MHz, although this is a crude : benchmark. Doing this could reduce the life expectancy of PCI : cards. Reduce the life expectancy? How? My experience has been that overclocked cpu's/cards either work or don't work from square one...they don't work and then fail. If you have different experience please share. I'd hate to think I'm risking expensive cpu's and #9 graphics cards... : : With 15ns cache and 70ns SIMMs I was able to run a DX4-120 with : 0WS and 2-1-1-1 cache burst read, the fastest settings supported. : This is probably motherboard dependent. I do the same. No problems. : : And, in case both statements are true, why bother looking : : at (X * 40)MHz 486 CPUs at all? : : They are more of a win with VLB motherboards. Yup. My play machine is currently a 486/120 with #9 GXE-64-Pro VLB card + 32mb RAM + ancient ISA SCSI card + quad speed CD-ROM and it is a screamer. Back of the napkin benchmarks (for me) put it at somewhere between a P75 and P90 in terms of performance and I was able to leverage "spare parts" to do it. Unless you're doing heavy number crunching, I've found that once you've passed Dx2/66 performance the cpu becomes almost irrelevant in terms of how "useful" a system is. Modern video and IO cards (major cycle stealers of old) usually now have enough "brains" to take their orders and run with the ball, leaving the cpu to worry about other more important tasks. When it gets to the point that P166 mboards cost as much as toasters, I'll go for more cpu brawn. :-) : : P.S. I don't own a PCI box, but just planning to buy one, choosing : : the best bang-per-buck configuration now. : : Was considering AMD 160MHz (glorified 486, called 5x86, he-he :) : : chip, which has 40MHz main freq and 4x multiplier. : : This is the 5x86-133, it's only 160MHz if you overclock it, and then you're : back where you started... Really....According to AMD's web page, it's almost identical in performance to a 486/120... : : Now I'm seriously considering AMD 133 part (this one is 33MHz, 4x). : : Guys have a very nice opinions on it. : : For PCI, the AMD 5x86-133 makes more sense. I'm running one now, : and very happy with it. I might try one for grins, but AMD's own benchmarks put it almost exactly where the 486/120 is...I'm not sure I understand their marketing... Chris -- Christopher Mauritz | For info on internet access: ritz@mordor.com | finger/mail info@ritz.mordor.com OR Mordor International | http://www.mordor.com/ 201/212/718 internet access | Modem: (201)433-7343,(212)843-3451