Page "DDR SDRAM" Paragraph 3

Compared to single data rate ( SDR ) SDRAM, the DDR SDRAM interface makes higher transfer rates possible by more strict control of the timing of the electrical data and clock signals.

Implementations often have to use schemes such as phase-locked loops and self-calibration to reach the required timing accuracy.

The interface uses double pumping ( transferring data on both the rising and falling edges of the clock signal ) to lower the clock frequency.

One advantage of keeping the clock frequency down is that it reduces the signal integrity requirements on the circuit board connecting the memory to the controller.

The name " double data rate " refers to the fact that a DDR SDRAM with a certain clock frequency achieves nearly twice the bandwidth of a SDR SDRAM running at the same clock frequency, due to this double pumping.