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If I need to choose only two differences i would choose the power comsumption and the speed difference:
1. Power consumption: Compared to DDR2 memory, DDR3 memory uses 30% less power. This reduction comes from the difference in supply voltages: 1.8 V or 2.5 V for DDR2, and 1.5 V for DDR3.
2. Speed: The primary benefit of DDR3 SDRAM over its immediate predecessor, DDR2 SDRAM, is its ability to transfer data at twice the rate (eight times the speed of its internal memory arrays), enabling higher bandwidth or peak data rates. With two transfers per cycle of a quadrupled clock signal, a 64-bit wide DDR3 module may achieve a transfer rate of up to 64 times the memory clock speed megahertz (MHz) in megabytes per second (MB/s).
Data mostly from Wikipedia. Sorry, no illustrations here.