Just got a new 21.5" iMac today. Tried installing 2x4gb sticks today for a total of 12gb, but no matter what I did it wouldn't recognize. My first attempt it didn't see the RAM (only showed 4gb in About This Mac and system profiler listed the other slots as empty), next few times at reseating the modules I just got beeps when I turned it on. Works fine when I leave it stock. This is what I got (x2): http://www.newegg.com/Product/Product.aspx?Item=N82E16820147068 I noticed that the stock modules were a few mm wider than the Samsung ones I bought. So...bad RAM or wrong RAM? EDIT: In case it matters, high-end 21.5" with the 2.8 i7 processor upgrade.