I installed a 512 mg ram chip in my rev A clamshell iBook, and it runs quite well. I purchased mine from MemoryX. I called to order a low profile 512 chip, and the sales girl mentioned a low power, low profile 512 mg ram chip. It cost $179.90 (about twice the cost of the regular low profile 512 chip.) I ordered the low power chip, installed it, and it runs fine. The machine recognizes all the ram. The battery life did not noticably decline! And it doesn't seem to be any hotter than with the 256 chip. I am quite happy with this purchase. I also had a 30 gig harddrive installed (by www.WegenerMedia.com), did the firmware upgrade, and then installed Jaguar. It's marvelous! Much faster than OS 9 or even OS 10.1. I highly recommend upgrading to Jaguar if your harddrive is large enough. Paula Rutledge