hi, i looked already at the previous posts and i did not see this posted already, so i felt it was safe. I just got an imac 800 15inch, and i looked in the system profiler and it says it has 512 memory on j13...i dont know if j13 or j12 is the user accessible memory slot. Im hoping its installed on the inside cause i would have the extra memeory to take it to its max of 1gig. if anyone knows how to tell the difference, please let me know! i would open the bottom, but im installing tiger as we speek...thankyou! -dave