I bought a Dimension 8100 P4 computer last August and Dell seems to be wrong about how much RAM it can hold. It's supposed to have only two DIMM slots but there are four. The first two slots have memory in them and the other two have blank cards in them. I'm told by DELL reps that I can only upgrade to 512MB so I bought two 256 sticks from MWAVE to upgrade from 128 to 512. I decided to take the two blank cards out after the upgrade and slip in the two original 64mb cards. The computer recognizes this extra memory and says I now have 640K. If the computer recognizes the memory then it must be using it right?