AMD64s are a bit confusing as far as the FSB goes.
They technically do not have a FSB, but an LDT or HTT (hypertransport) bus because the memory controller is built directly into the chip. On previous chips the FSB acted as a communication link between the controller and chip but since that is no longer neccesary the high speed, low latency bus directly between the chip and RAM was created.
The HTT is pretty much Memory Speed * LDT Multiplier * 2
Which on AMD64s on socket 939 would translate into:
200 * 5 * 2 = 2000MHz
And since as you may know DDR is double date rate memory the multiplication by two at the end is technically doubling the RAM speed so technically speaking the "FSB" speed or HTT speed is 1GHz.
But to answer your question, AMD64s use DDR400 PC3200 memory
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