I have a 867Mhz Powerbook G4 with 640Megs of RAM. When I bought the computer, this was as much RAM as you could put in the unit. However, I'm wondering if this limit was due to the high prices for a 1 gig stick of RAM at the time, or if there is a limitation on the motherboard itself. Sorry if this is addressed elsewhere, I honestly tried searching for the answer first.