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For your quick comparison between the two memeories....
Data Bus >64 bits 64bits
Data Rate> 200/266/333/400 Mbps 400/533/667 Mbps
Bus Frequency> 100/133/166/200 MHz 200/266/333 MHz
DRAM Frequency> 100/133/166/200 MHz 100/133/166 MHz
Package Type> TSOP-II FBGA
Densities>256MB 512MB 1GB 256MB 512MB 1GB
Voltage> 2.5V 1.8V
Prefetch Size> 2 bits 4 bits
From this chart you can tell that DDR2 effectively picks up where DDR1 leaves off. It's data rate begins at 400 and scales upward to 667 currently. Another thing to take notice of are the latencies; they are double those of DDR. Apparently, they are sacrificed for the higher speed, and it should be interesting to see what kind of a trade off it is.
Voltage requirements for DDR2 are greatly reduced from that of DDR. Down to 1.8 volts; this translates into a lot less power needed to read and write for the memory