Bests & Worsts Reviews from Amazon

I initially installed this memory in the already-open slots 1 and 3 (the factory RAM was in slots 2 and 4) and got 3 beeping sounds and no bootup. After following the advice of another reviewer here, I turned it back off, opened the memory compartment back up, and swapped the positions of the factory RAM and the Crucial RAM so it went like this: Slot 1: 4GB Apple RAM (Top slot if iMac is upright) Slot 2: 8GB Crucial RAM Slot 3: 4GB Apple RAM Slot 4: 8GB Crucial RAM (Bottom slot if iMac is upright) That worked fine and I now have 24GB of RAM installed on the Late 2012 27" iMac. Tip 1: the Crucial RAM is a tight fit in the memory slots. To get them back out to swap their positions, I first had to remove the Apple RAM so that I could get a better grip on the Crucial RAM. Tip 2: I had difficulty getting the memory access panel off of the iMac because my finger wasn't going far enough in to depress the button all the way. I used a small key (a screwdriver would work too) to push the button in all the way to get the access panel to pop open.