One common question is if these modules would work on previous G4/AGP motherboards. The connector is said to be the same based on appearances (unknown as far as actually pinout). Of course the dual G4 systems have a much larger heatsink as shown in this photo:

Note the small heatsink at the rear of the motherboard, said to be attached to the Gigabit Ethernet chip.

Update: A reader I trust wrote to say the new MP G4 modules do work in the original G4 motherboards:

" Mike,
The dual processor cards Apple's shipping now do work in older Sawtooth machines. The pinout of the CPU card connector is unchanged. I've seen an older Sawtooth G4 using both CPUs with one of the new dual-processor cards installed.

For such a transplant to work, you must get both the card and the heatsink. A single-processor Sawtooth heatsink won't even make contact with the CPUs on the dual processor card. [This is noted and shown above-Mike]

-- Tim Seufert "