Hi guys, I have had the same problem reported elsewhere in this forum since I got my new 15" HiRes Powerbook in Dec 2005: upgrading the standard 512 MB RAM with non Apple RAM produces random freezes. Apple checked the pb, they confirmed the freezes, thought it could only be a faulty logic board, Apple exchanged the pb for a new one, I ordered another GB of RAM from APlus, it freezes. I returned the RAM to my dealer, he sent me another module, this time from Nanya, same happened again. Next, I ordered genuine Kensington RAM, same thing. The pb runs fine if I have only the original 512 MB genuine Apple/Hitachi module installed. Let me point out, 1) that I encounter these freezes even if nothing else except OS X (10.4.x) has been installed; 2) Hardware test does not report a faulty RAM despite the freezes 3) I can reproduce the freezes very easily; Apple Tech Support was absolutely clueless and useless. I would be very, very grateful if someone could give me a hint how to rectify the problem. Robert Ros, Ph. D.