What is ddr2-400 or ddr2-533?

Answer 1

Goto http://en.wikipedia.org/wiki/DDR2_SDRAM. Scroll down a bit til you see chips and modules. But for those that are less computer literate: DDR2: the type of memory. -400 -533, etc.: the speed of that memory. The numbers represent a certain specification within that type of memory. Higher number=faster. So if your Motherboard supports both and youre trying to decide which to buy, get the 533. It's a bit more expensive, but you'll get much better performance.