When I look at "About This Mac" it says that I have a 2.4 GHz Intel Core 2 Duo. I originally had two 1GB sticks. When I installed two 2GB RAM sticks, it wouldn't boot. Just for fun, I tried putting one 2GB and one 1GB stick inside, and it boots fine. crucial.com says that I can have up to 4GB: http://www.crucial.com/uk/store/listparts.aspx?model=iMac 2.4GHz Intel Core 2 Duo (20-inch - 667MHz) But the guides say that it depends on if I have Merom w/ Santa Rosa chipset or not: http://guides.macrumors.com/Understanding_Intel_Mac_RAM But I read somewhere else that even if I install two 2GB sticks that it will just ignore the power of the second one and default to 3GB. Any help anyone can provide would be great. I'm fairly new at this sort of thing.