When I bought my computer(Acer 6120 pent 400) it had a 64MB Ram module(168Pin 10ns 3.3volts) in 1 slot of 3 slots. Then I purchased another 64 MB from Frys a while ago that says on reciept 8ns/L SD 3v 8chip unbuffered w/ Eprom PC -100 CERT 440 BX(WHATS THE L SD MEAN?) and put that in next slot. Things seemed to work fine. Now I just ordered some Kingston value memory 128 MB PC 100 non ECC DIMM CL2 memory to put in last slot. Now does the order of the slots matter by which one stick of ram would get used more often? and is there a program that will test all your ram and make sure its all working right? Is there that much difference between 10ns and 8 ns? I take it if you have a 10ns and a 8ns then they will both run at 10ns? If you can help me understand this a little better most appreciated. Thanks again.