Hi- I was wondering if I purchase 4gb of Memory for my MacBook Unibody 2.4ghz, can I then move the 2gb from my Macbook Unibody to my friend's white macbook (1.83 Ghz Core Duo.) Currently his computer has 512mb of DDR2 SDRAM. Is his computer compatible with DDR3 memory? If not will it take the DDR3 and run it at DDR2? Pretty much I am wondering if I could just move the memory to his computer and it will be better then what he has. I guess my general question is DDR3 backward compatible with DDR2? Thanks!