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Originally posted by Z-man:
I managed to figure out that PC 3200U and PC2 3200U are not the same. They have different pins. Can someone explain the difference?
PC-3200 properly known as DDR-400.
PC2-3200 known as DDR2-400
The number after PC refers to theoretical bandwidth. The number after DDR refers to the memory clock (or less accurately, speed). DDR means Double Data Rate, that is for every clock cycle there are 2 data transfers, so DDR with a 200Mhz memory clock would have a 400Mhz "speed". So it is refered as DDR-400. DDR2 does 4 data transfers per cycle, so theoretically can move twice as much data at a given latency. The doubling of data operations/cycle necessitates the different pinout.

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...Since the CPU bus is 800, should I only be using the the 3200 RAM? or can I see a gain, or at least the same performance out of the 5300 RAM. I have two gigs of the 5300 RAM.
There are respected experts that insist you get a performance edge by using even multiples - such as 3.2 gig CPU, 800Mhz bus, 400Mhz RAM, etc and they do have a point and several tests to back them up. I don't know the difference in everyday business computing. In home computing, maybe it makes more sense, because believe it or not the average home PC is taxed much more than a work PC because of all the multimedia, streaming, graphical games etc.