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Re: PCI bus speed on OldWorld PCI macs

On   1 Aug, this message from Michael Hackett echoed through cyberspace:
> On Thu, 1 Aug 2002 16:50:41 -0400 (EDT)
> "Albert D. Cahalan" <acahalan@cs.uml.edu> wrote:
>> Michael Hackett writes:
>> > No, because you can't change the PCI clock.
>> Do you know this specifically for his hardware? Remember that
>> it is 100% allowed to run PCI at less than 33 MHz, and that
>> this is common.
> Ah, well, I've never heard of that on the Mac side, but that may be the
> case. From everything I've read, the PCI clock was independent of the
> system bus clock, but nothing's to say that information wasn't wrong.

No, you're right. The PCI clock is fixed at 33 MHz.

> Can you point me to a source for more info?

Look for this here on Apple's developer site:


Also, Apple technote 1008 is of interest.

> Regardless, the fact remains that any PPC Mac has plenty of PCI
> bandwidth for megabit Ethernet.

Well, I'm having problems with a 100Mb/s Ethernet on my 7600. Remember
that 80 MB/s is the absolute maximum according to Apple
_under_optimal_conditions... meaning using 'Read Multiple' and 'Memory
Write & Invalidate' PCI commands for the card's DMA operations. No idea
what the RTL8139 on my card really uses....



Michel Lanners                 |  " Read Philosophy.  Study Art.
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email   mlan@cpu.lu            |
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