On Sun, 11 Jan 2004, Ronan Cunniffe wrote:
> So a "64-bit" PCI slot is 32-bit address, 64-bit data? I thought a
> 64-bit device could access all of 64-bit memory.
that's the width of the bus. For backwards compatibility, 64bit
addresses are transferred over 2 clocks, aka Dual Address Cycle
(DAC). (increased overhead too). (there might be some variants of
PCI-X that can do 64bit addressing single-cycle, but googling proved
inconclusive).
> If PCI is explicitly 32-bit, then WTF is the point of sticking a
> 64-bit chip in there?
Thats why all real 64bit arches have IO-MMUs. Removes overhead of DAC
too.
> Ronan
regards,
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