SD Ram is actually SDR SDRAM, and DD Ram is actuallyDDR SDRAM, though the former does not usually have theSDR in front of it. The letters SDR and DDR stand for SingleData Rate and Double Data Rate, and the letters SDRAMstand for Synchronous Dynamic Random Access Memory.The main difference between SDR and DDR memory isspeed. There are a lot of little differences, but the main one(IMHO) that affects the user is speed: DDR can transferdata at roughly twice the speed of SDR. More speedy datarates = better performance. Just remember, themotherboard you are using must include the appropriatechipset to support the different RAM types. They are notinterchangeable. SDR SDRAM comes in three main flavors:PC66, PC100 and PC133. Each successive number refersto the bus speed of the RAM in MHz, thus PC66 runs at 66MHz, PC100 runs at 100 MHz, etc. SDR SDRAM has 168pins at the connector.
DDR SDRAM has 184 pins at the connector, which is onereason you cant just use DDR instead of SDR, and comesin many different flavors; PC2100 which runs at 266 MHz,PC2700 which runs at 333 MHz, PC3200 which runs at 400MHz, etc. In order to know which type of RAM you need, youmust know what your motherboard supports. I recommendsearching the motherboard manufacturers website for thisinfo, or review sites like www.tomshardware.com orwww.sharkyextreme.com .