max bus speed in PCI-X

[Prateek Sharma <Prateek.Sharma@dcmtech.co.in>]

Hello PCI experts,

By introducing PCI-X 133 MHz specifications, though we have doubled the peak
throughput, but when it will be actually implemented in the systems, do we
hope to get this much bandwidth?

Specs say that Max bus speed is chosen when system board is layed out.

*1 connector = 133 Mhz
*2 connectors = 100 Mhz
*4 connectors = 66 Mhz

Lets say I design a board keeping in mind future expansion and make a
provision of 4 connectors.
But I plug-in only a single card, which is 133 Mhz capable. Is the bus going
to operate at 66 Mhz even though there is a single card sitting on it???

And regarding a PCI-X to PCI-X bridge, lets say primary interface operates
at 133 Mhz. Since PCI-X is backward compatible, and secondary interface
frequency will depend on the number of connectors, will design of the bridge
depend on the system board? whether secondary interface has to work on PCI
33, or PCI-X 66 or PCI-X 133 Mhz?


Thanks and regards



Prateek Sharma
Design Engineer
ASIC Design
DCM Technologies 
http://www.dcmtech.com