Hi, I have an IBM thinkpad laptop right now fitted with one(1) stock 256MB PC2100 SO-DIMM and has one more memory bay available. The processor is a Pentium4 at 1.6 GHz with 400MHz front side bus, and I’m running Windows XP Professional. I’m only using the notebook at about computer novice level – web browsing, MS Wording/Powerpointing, IMing w/ webcam, listening to music, downloading – sometimes all of them together, but nothing like heavy game-playing or running servers . Right now it works fine overall, with some slowing down occasionally (especially when running viruscan). I'm not looking for it to be craaazy fast, so I thought maybe I’ll add another 256MB, but not sure if you guys think there'll be obvious improvement? Actually, my real question in this posting is about the PCxx00 ratings. Since the laptop has 400MHz for FSB, correct me if I’m wrong, I can put any of pc2100, 2700, or 3200 in the empty memory bay and the system can run as high as 400 MHz (266 and 333 for the first two of course). But if I leave the stock pc2100 memory in the other bay running at 266MHz, would the overall performance still be stuck at the lower of the two RAM speeds? Or is there an additive effect... I guess I’m just unclear which would be more beneficial: increasing the PC number or increasing the MB size? Thank you.