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DDR RAM runs at the exact same clock speed as normal SDRAM. But, as batmeat pointed out, the DDR can transfer data on both the rising and falling edges of the clock signal, while SDRAM can transfer on _either_ the rising _or_ the falling edge (I want to say it's the rising edge, but I'd have to look at datasheets to be sure). But not both edges.
So the DDR memory subsystem itself runs faster, but the rest of the computer is still at whatever frequency it ran at before.
Put another way, the memory throughput is theoretically doubled (theoretically because there are practical limits on the speed, too), but the rest of the system is still the same.
Bryan
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