First of all latency refers to delays in transmitting data between the CPU and SDRAM. It is better to have s smaller latency value (denoted as CL). The main difference between DRR,DRR2 or DRR3 is the notch position on the ram slot. That's why a DRR3 ram slot will never fit on a DRR2 motherboard. Furthermore, DDR2 and DDR3 are improvements on the same technology and further increase the number of data transfers per clock cycle. DDR2 RAM provides 4 data transfers per cycle, while DDR3 increases the number to 8. Finally, pin configuration comes with the difference between the type of DDR slot. For example, a DRR3 will have a different pin configuration from a DRR2 slot. Pin configuration is not an important subject to worry about.http://www.scan.co.uk/products/4gb-corsair-ddr2-memory-800-mhz-2x240-dimm-unbuffered-cl5http://www.scan.co.uk/products/4gb-(2x2gb)-corsair-twinx-xms2-ddr2-pc2-6400-(800)-240-pins-non-ecc-unbuffered-cas-5-5-5-18-dhx#ProductFeatures
Hope this helps!