I have a MacBook 2.4GHz Core 2 Duo model 1181 (Penryn). I understand that this model can only address a maximum of 3Gb of RAM. If I want to upgrade my RAM, can I replace just one of the two 1Gb chips to a 2Gb chip in order to obtain the maximum 3Gb addressable? Or do I need to upgrade both of the 1Gb chips to 2Gb chips? In other words, is it necessary to have symmetry between the 2 RAM chips, or will a combination of one 1Gb chip and one 2Gb chip work correctly? Thanks!