Quote from an article on the topic, it's about ram in general and also discusses ddr3. It may be more about PCs, but computer components are computer components.
DDR2 (Double Data Rate 2) memory has been available for quite some time. New computers, even computers released within the last three years or so come equipped with DDR2 memory. An improvement over DDR memory, DDR2 produces faster performance with less energy consumption.
What about ROM because I've read that the bionic has 2GB of ROM how does that affect the performance of the phone. The EVO 3D has 4GB of ROM(I heard this on one of the hand-on videos) and it ran htc sense really smooth possibly the smoothest I've seen a UI run on an android device. Did the 4GB of ROM hav to do with that?