My friend has this model of iMac.. and I have tried to put 2x 8GB sticks into it to replace the 2x 2GB of OEM.. Supposedly, from any and all info I can find, it is capable of recognizing and using 16 GB of RAM, but is there ANY reason that it must be configured as 4x 4GB perhaps, as opposed to the 2x 8GB Sticks I am trying now..?? ** When the RAM is inserted, it powers up and NEVER goes past 'the Start-Up Apple' mid-screen.. and I have tested the RAM, it does work fine in my 2011 MBP, which uses the same spec RAM.. Thanks you for any and all replies.. if someone can help much me to cipher this one, much appreciated.. Have a Great Day!!