DDR <> DDR 2 <> DDR 3 SO DIMM
Q: Are DDR and DDR2 SODIMM memory modules compatible?
A: No. DDR2 memory modules have basically the same dimensions as the DDR modules, but because of different voltages and pin configurations, DDR2 modules have a different "key" or notch in their connector to prevent them from being plugged into an incompatible socket. DDR2 memory modules will only fit in systems and motherboards designed to specifically support DDR2 memory. A DDR2 SODIMM will not fit in the DDR memory slot.