DDR stands for Double Data Rate and is a kind of SDRAM. Hence it is also sometimes called DDR-SDRAM or SDRAM II as well. The DDR computer memory can receive and send signals twice per clock cycle which makes it twice as fast as an SDRAM, hence the name double data rate. This advanced version of synchronous dynamic random access memory uses the falling and rising edges of the incoming clock signal rather than waiting for the clock signal before responding like SDRAM. As such, a DDR chip is able to send out and receive more data in a single cycle as compared to SDRAM, making it much more efficient as it consumes comparatively less power as well.
In order to make the timing of the clock and the response more accurate, one may put to use a phase locked loop or self calibration techniques. Since the DDR increases data transfer rate by increasing the amount of data transferred in a cycle only, the frequency remains the same, reducing the signal integrity requirements. The newer versions of DDR are known as DDR2 and DDR3. where the DDR module uses a 184 pin connector, the newer versions use 240 pin dual inline memory modules. To introduce further improvement onto these existing models, quad data rate pumping modules are also set to be released, pumping out four data points in a single clock cycle.
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