Date: Thu, 9 Jan 1997 15:20:06 +0000 (GMT) From: Mark Powell <M.S.Powell@ais.salford.ac.uk> To: Michael Smith <msmith@atrad.adelaide.edu.au> Cc: freebsd-scsi@freebsd.org, freebsd-scsifreeb@sdorgsd.org Subject: Re: Can the P/I-P55T2P4 be overclocked? In other words does it support 75 and 83MHz bus speeds? Message-ID: <Pine.BSF.3.95.970109150900.21964A-100000@plato.salford.ac.uk> In-Reply-To: <199701091208.WAA26952@genesis.atrad.adelaide.edu.au>
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On Thu, 9 Jan 1997, Michael Smith wrote: > Mark Powell stands accused of saying: > > > Correct, only the plain P55T2P4 rev. 3.0/3.1 have everything needed to do 75 & 83Mhz, > > > but I seriously doubt that a heavily loaded 2940 will perform well above 33Mhz PCI bus > > > speeds.... > > > > Why's that? Also, what d'you mean by "well"? > > A good question. Providing the bus interface on the aic7xxx part is > up to it, it might run faster. Bear in mind that it's only designed > for 33MHz though. Yeah. The guy replyed saying that Asus have tested the 7880 and found that it doesn't meet all their test criteria over 33MHz. Although it does "work". > > > The SC-200 and the SC-875 stand a much better chance of running well at higher PCI > > > bus speeds when drives are attached that fully use their capabilities. > > > > Not too sure on the quality of the FreeBSD drivers for the NCR though. And > > The FreeBSD NCR drivers are excellent. Note that experimental > evidence tends to indicate that the 2940 is better under multi-drive > loads than the NCR, but by a fairly small margin. Also note that many > so-called "onboard 2940" controllers are actually lower-spec parts > that won't perform anywhere near as well. The P55-T2P4S motherboard has a 7880 on-board. However, that motherboard won't go to 75MHz and 83MHz as will the non-SCSI T2P4. > > I don't think the NCR 53c875 is supported at all, just 810 & 825 :( > > The FreeBSD/NetBSD NCR driver supports the 810, 815, 820, 825, 860 and > 875. > > > Suppose, I could just use narrow drives instead of the wides I > > currently have? Hmmm, I really wanted to overclock a Cyrix 6x86 > > P166+ to a P200+, and this seemed to be the way to do it from > > other's expericence. > > Why? Unless you are going to be doing things that are totally CPU > bound, you should be more worried about memory and I/O throughput than > plain CPU cycle time. Going to narrow drives will just defeat this. Yeah, I know. I meant if the 875 wasn't supported I could use the 810 with narrow drives and still push the external clock speed to 75MHz. However, now you've enlightened me I can get the 875 and use it under FreeBSD with my wide drives and hopefully with a greater chance of success than with a 7880. > > Do you have any idea whether the DFI G586VPS Pro (using VLSI Lunx chipset) > > or the or the MTech R534 (http://www.mtiusa.com/r534.htm), using the > > Sis5571 chipset which I think I read somewhere "allows the PCI bus to be > > locked at 32MHz [sic?] whatever the external clock speed", would be better > > for this purpose? > > I would be demanding datasheets on the chipsets in question and > studying the timing values programmed by the BIOS for these boards in > comparison with the Intel chipsets and their recommended timing. The > 430FX chipsets push things pretty hard already; I'm skeptical that > these other newcomers are likely to be more than marginally better. These chipsets are designed to accomodate the Cyrix P200+ which needs an external clock speed of 75MHz. They also support the Cyrix's "Linear Burst Mode" which can supposedly give a 3-5% speed improvement on cache filling. However, I agree and think I'd be going down a blind alley with such new chipsets. I'll stick with the 430HX chipset on the T2P4. Mark Powell - Unix Information Officer - Clifford Whitworth Building A.I.S., University of Salford, Salford, Manchester, UK. Tel: +44 161 745 5936 Fax: +44 161 736 3596 Email: mark@salford.ac.uk finger mark@ucsalf.ac.uk (for PGP key) <A HREF="http://www.ucsalf.ac.uk/~mark/">Home Page</A>
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