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Date: Sun, 14 Dec 1997 17:06:17 -0600
From: Allan Alford <aa@jump.net>
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To: Tom <tom@sdf.com>
CC: Marc Rassbach <marc@tandem.milestonerdl.com>, freebsd-hardware@freebsd.org
Subject: Re: Speed of the cards? was Re: SCSI card to choose
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Tom wrote:
> 
> On Sun, 14 Dec 1997, Marc Rassbach wrote:
> 
> > As I am looking at overclocking my bus speed, which cards (SCSI and network)
> > out there are known to work at faster bus rates?  (75 and 83 mhz bus)
> 
>   It seems that you are talking about CPU memory bus speeds, that is the
> base rate of the CPU.
> 
>   PCI gives you 132MB/s bandwidth.  Anything different is not PCI.
> 
> Tom

The way I understand it is this:

PCI bus speed = 1/2 motherboard bus speed.  Motherboard bus speed is the
same as 'CPU speed' without the clock multiplier.  The newest
motherboards
that are breaking the 66MHz speed barrier have increased the PCI bus
from 33
to either 37.5 (half of 75) or 41.5 (half of 83).  The official PCI
standard
was designed to accomodate up to 66MHz, but only specifically calls for
33MHz
in its current iteration.  Thus, with the newest motherboards, many PCI
cards
of older and/or less reliable manufacture do not work properly.

To my knowledge, Cyrix is the only CPU manufacturer currently active who
can support the 83MHz standard anyway.  Because of their new chip, a
handful
of motherboard manufacturers are now claiming support for that speed. 
What
the individual PCI card manufacturers are officially stating, I do not
know.

This is very new and very cutting edge technology.  Research well.

- Allan