On  3 Nov 98 at 18:33, Dennis Noble wrote:

> I am setting up a system with a PC Chips M577 Motherboard and am
> setting it up as 75MHz X 4 for an AMD K6 -2 300MHz CPU. (It will
> not work at 100MHz X 3 with this series of CPU and MB).
>
> The question that I have, is that this MB has two 75MHz settings.
> One has (PCI 37.5M) under it and the other (PCI 30M) what are these
> settings for ? Would I be better just setting it at 66MHz X 4.5?

  On many motherboards, the speed of the PCI bus is simply half the
speed of the main bus.  This is nominally 33 MHz for a 66 MHz board.
  At 75 MHz, such halving runs the PCI bus at 37.5 MHz.  Some of your
PCI peripherals may be quite happy at 33 MHz, but start to fail at
37.5 MHz.  IF you find you have such a problem, you may be able to
get around it by running the PCI bus "asynchronously" -- that is, at
its own frequency unrelated to the main bus frequency.  This is
apparently what the "30M" setting is for; use it only if the 37.5
setting doesn't work.
  [Most 100 MHz boards divide that frequency by THREE to clock the
PCI bus at 33 MHz.]

David G

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