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PCI On-card Trace Length
My question involves PCI 2.2, and the 1.5 inch limit for trace lengths
on PCI add-in cards for 32 bit buses, and the 2.0 inch limit for the 64
bit extension signals. Electrically speaking, why is the 64 bit bus
trace length allowed to be longer than the 32 bit bus signals.
Physically, one can see that the traces must be longer just to reach all
of the connectors, but what electrical justification allows the longer
length for just that portion of the bus. Are there less taps allowed on
64 bit buses, similar to less taps allowed at 66 Mhz?
Does that mean that if there will be a limited number of add-on cards
(and slots) allowed per PCI bus, that the 32 bit bus trace length can be
lengthened to the same limit as the 64bit bus, and still be "PCI
compliant"? Many thanks