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Re: PCI bus speed on OldWorld PCI macs

Chris writes:

> 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.

100 Mb/s needs a 3 MHz PCI bus, or maybe 10 MHz if you
allow for a seriously inefficient motherboard.

> -what is the speed of the PCI bus on an older powermac?  (is is 50% bus speed?)
> -If I clocked up my PowerMac 7300/180 (45mhz bus) to 175 to 200 mhz on a 50mhz+
> bus would I be getting a faster PCI bus as well?

Your bus is most likely one of:

a. locked to 33 MHz
b. at 22.5 MHz, due to a 2:1 clock ratio
c. at 30 MHz, due to a 3:2 clock ratio

Speeds above 33 MHz are not allowed. PC hardware
commonly ran PCI at 25, 30, and 33 MHz.

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

You might get faster crashes.

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