How many pins are on DDR DIMM modules?
Sometimes its 184 Pins
There is a notch that prevents installation, even though the modules are the same size and have the same number of pins. Notch position between DDR and DDR2 are diferent. Also, the memory socket on a motherboard is diferent for all types of memories. If the memory socket is design for DDR you can't put any other memory type but DDR and so for all other types.