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Re: PCI bus speed on OldWorld PCI macs

On Thu, 01 Aug 2002 13:50:07 -0500
Chris <cmarcoe@mail.nasboces.org> wrote:

> Pardon my ignorance but in a conversation a while ago someone asked
> this listserve if upgrading to 100mbs ethernet on an older PCI
> powermac lab would be worth it to improve terminal performance.
> Most people seemed to say 'NO' because of the limits of the PCI bus.

100Mbps Ethernet = approx. 10-12 MB/s. PCI bandwidth is 132 MB/s (or
80-90 MB/s in practice, I've read here recently). Plenty of headroom. I
doubt such a card would even get much in the way of other PCI traffic.

In short, the answer is 'YES', a faster Ethernet interface will improve

> -what is the speed of the PCI bus on an older powermac?  (is is 50%
> bus speed?)

As Ben said, it is 33 MHz. It has no relation to the system bus speed,
and remains the same even if you overclock the system bus.

> -What about the onboard video and ethernet?  Is that effected
> performance wise by the increased bus speed?

Video possibly, but keep in mind that on-board Ethernet is only 10Mbps,
which is only about 1 MB/s throughput at the best of times, hardly a
significant load on the system bus.

> -Should I worry about old PCI cards not working at "overclocked" PCI
> bus settings on the PPC-MAC side?

No, because you can't change the PCI clock.

-- Michael

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