Hi, I have a MacBook. (not sure which one. the one right before the macbook air came out.) and a 21 inch iMac. (I belive the 2010 model.). I want to get change it so that both have more RAM. The MacBook has 2 GB and the iMac has 4. Can I buy 2 4 GB RAM cards for my iMac and put the old iMac cards into the MacBook? Basically, are all of Apple's RAM cards the same and exchangeable between different Apple computers?