From OWC: "While Apple lists 4GB as the maximum amount of installable memory, our 8GB memory kit OWC8566DDR3S8GP is now tested and fully certified for the full 8GB utilization a real performance benefit for memory intensive application loads. While we were at it, we also tested another brand 8GB memory kit and found it consistently caused kernel panics and non-boot issues. Even though both are the same spec of DDR3 1066MHZ SO-DIMM, sometimes quality does have its result."