Yes, 168 pin and 72 pin memory modues are different, you need to know which ones your motherboard takes More likely 168 for newer motherboards.


Not sure about RDRAM only working with P4, but I do know it only works in Pentium chipsets, so it wouldn't work with an Athlon processor.



PC100 and PC133 tell you the max speed of the bus supported by that RAM at it will stay stable at - PC100 for a 100MHz bus, PC133 for a 133MHz (faster) bus. Again, it's best to know what your motherboard bus speed is - there's no point getting PC133 RAM for a 100 MHz bus, since it'll only operate at 100 MHz then, unless you plan to upgrade that motherboard in the future or something.

CAS or the latency of the RAM kind of measures the speed at which data can be read/written to (not quite though, but I don't fully understand it myself), in ms - so the smaller the better. I think my RAM is CAS3 but I've explicitly told the BIOS treat it as CAS2 - it'll be my fauilt if I get memory read.write errors, but I've yet to have any and had it set at that for months now