Don't get snookered when buying memory for an older system.
Example: Samsung KM440S16030CT-GL
-GL means PC100/CL3
-GH means PC100/CL2
-G8 means PC133/CL3
-G7 means PC133/CL2
CL2 is ALWAYS better than CL3. PC133 is only better than PC100 if you are able to clock your bus higher than 100MHz. On i440BX systems as an example, this is undesirable because the AGP bus will be overclocked (the smallest ratio available on BX is 2/3). So when upgrading RAM, get PC100 CL2, or -GH in that case.
I am not sure whether PC133/CL3 (i.e. 8ns) memory can be safely run at CL2 in a PC100 board.
Many people posting memory on eBay are GUESSING as to its performance characteristics. Make sure you know before you waste money bidding on something that isn't really worth that much.