Ok, DDR-SDRAM is an updated model that transfers data twice as fast. It fits in a different socket though, so you need a different motherboard (unless you have the Asus A7A266 or the ECS K7S5A, which support both types).
PC100 runs at 100MHz and PC133 runs at 133MHz, right?
DDR200 and DDR266 (more commonly known as PC1600 and PC2100), are basically the DDR equivalent of those.
PC2400 is double 150MHz, and PC2700 is double 166MHz.
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