Difference between SDR SDRAM and DDR SDRAM

The conventional SDRAM modules and DDR SDRAM modules have the same basic lines, as can be seen in this picture. It is still difficult for the uninitiated to spot the difference between the two DIMM's. SDRAM (above) has two notches, whereas DDR SDRAM (below) only has one. If you have an MSI Pro266 Master or a Shuttle AV32, it's a good idea to take a good look at your board slots. Both boards have SDR DIMM slots and DDR DIMM slots. It's easy to confuse the two if you don't pay close attention to the notches.