the_punkinator is kind of right.
The following is an excerpt from an old post I did.
"Using the Q6600 as an example, the FSB frequency is 266 MHz. The matching DDR2 memory clock for that frequency is 533 MHz (266 X 2). DDR2 memory transfers two chunks of data for each bus cycle, hence double the frequency. Each bus cycle generates 2 memory clocks. So, to run 1:1 at an FSB of 266 MHz, we need DDR2-533 RAM.
What CPUZ does is a little confusing. It will tell you that the memory frequency is 266 MHz for a 1:1 ratio. "
In the computer business, there is a big difference between frequency and clock.