If you are curious as to what the difference between DDR2 and DDR3 is, OCModShop has published the perfect article for you.  The increase in maximum speed is the real difference, but if you are looking to find out how that is achieved, and why DDR2 can’t just keep be pushed faster then dig into the article. 
“DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is the name of the new DDR memory standard that has been developed as the successor to DDR2 SDRAM.

The memory comes with a promise of a power consumption reduction of 40% compared to current commercial DDR2 modules, due to DDR3’s 90 nm fabrication technology, allowing for lower operating currents and voltages (1.5 V, compared to DDR2’s 1.8 V or DDR’s 2.5 V). “Dual-gate” transistors will be used to reduce leakage of current.”

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