How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
NEMIX RAM 16GB (2x8GB Upgrade) DDR3-1333 PC3-10600 204-Pin SODIMM Memory for Apple MacBook Pro Early/Late 2011, iMac Mid 2010 27 inch 4-Core, iMac Mid 2011 21.5/27” , Mac Mini Mid 2011 at Amazon.com
iMac Intel 21,5" Late 2011 (EDU) EMC 2496 - used original spareparts for Macs
iMac Mid 2011 (21.5 – inch and 27 – inch) RAM Upgrade Dallas – Apple Mac Computer Repair Dallas , Laptop ,Desktop ,iMac ,MacBook iPhone iPad Data Recovery ,Virus
install - Installing and Upgrading Ram on a mid 2011 iMac (different size RAM) - Ask Different