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From: "Serge A. Babkin" <babkin@hq.icb.chel.su>
Message-Id: <199710051540.VAA09237@hq.icb.chel.su>
Subject: Re: PCI slowness ?
To: rjs@fdy2.demon.co.uk (Robert Swindells)
Date: Sun, 5 Oct 1997 21:40:11 +0600 (ESD)
Cc: hackers@freebsd.org
In-Reply-To: <199710051035.LAA00326@fdy2.demon.co.uk> from "Robert Swindells" at Oct 5, 97 11:35:25 am
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> 
> 
> > The chipset is Intel Triton on some chineese motherboard
> > with 75MHz Pentium, memory is 60ns EDO. 
> > Theoretical PCI throughput is 33M
> > of 4-byte transfers per second (the card claims to work
> > in burst mode). Theoretical memory throughput is at least
> > 10M of 4-byte transfers per second if we suppose that
> > the memory cycle with all overhead is 100ns and the
> > card reads by 4 bytes at a time. But the experiment
> > shows throughput of only 17MBps or 4.25M of 4 byte
> > transfers. Does the processor eats all the remaining 
> > throughput (although I think it must load most of the
> > code it runs at idling into the cache) ?
> 
> I thought that a 75MHz Pentium ran the PCI bus at 25MHz, not 33MHz.
> 
> Are you sure that the bus on your system is at 33MHz ?

No, I am not. But the motherboard has possibility to generate 33MHz
and if I were the designer of this card I would use this clock
independently of the processor clock. 

-SB