I should probably make a sticky on this, since this question has been asked at least 6 times in the last few weeks.
The Intel uses a quad pumped FSB; it's actually 2 x DDR busses running 90 degrees out of sync. As a result of that, whatever the FSB is rated at, you simply divide that number by 4 to determine the true, non-DDR, clock speed. So what you end up with is a true clock speed of 266MHz. Since it is a DDR bus that makes it 533MHz. Since there are two of them, you now have 1066MHz. The fact of the matter is that nothing about FSB and RAM requirements have changed with the C2D, and are exactly the same as the P4.
To have a 1:1 match for a 1066MHz FSB you need DDR2-533MHz (PC2-4200). Since the memory is dual channel, with two sticks you get your matching 1066MHz.
When the FSB moves to 1333MHz you will then want to use DDR2-667MHz (PC2-5300).
Code:
Actual FSB Clock Rated FSB Clock Min. RAM Needed
100MHz 400MHz DDR PC1600
133MHz 533MHz DDR PC2100
200MHz 800MHz DDR PC3200
266MHz 1066MHz DDR2 PC2-4200
333MHz 1333MHz DDR2 PC2-5300
* Intel skipped from 133MHz to 200MHz, so a 166MHz FSB was never implemented. If it had been, DDR PC2700 would have been used. A 1600MHz bus has not yet been implemented, but if/when it is, DDR2 PC2-6400 would be required.
** The above values are based on running a 1:1 syncronous RAM/FSB. It is possible to use RAM that is faster/slower using the memory dividers to run the RAM/FSB in asyncronous mode.
