Stands for "Double Data Rate 2." DDR2 RAM is an improved version of DDR memory that is faster and more efficient. Like standard DDR memory, DDR2 memory can send data on both the rising and falling edges of the processor's clock cycles. This nearly doubles the amount of work the RAM can do in a given amount of time. DDR and DDR2 are also both types of SDRAM, which allows them to run faster than conventional memory.
While DDR and DDR2 have many similarities, DDR2 RAM uses a different design than DDR memory. The improved design allows DDR2 RAM to run faster than standard DDR memory. The modified design also gives the RAM more bandwidth, which means more data can be passed through the RAM chip at one time. This increases the efficiency of the memory. Since DDR2 runs more efficiently than standard DDR memory, it actually uses less power than DDR memory, even though it runs faster. The only downside of DDR2 memory is that it is not compatible with standard DDR slots. So make sure your computer supports DDR2 RAM before upgrading your memory.