How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
Timetec 32GB KIT(4x8GB) Compatible for Apple DDR3L 1600MHz PC3L-12800 CL11 for iMac (Mid 2011, Late 2012, Late 2013, Late 2014 Retina 5K, Mid 2015 Retina 5K) SODIMM Memory Module MAC RAM Upgrade at Amazon.com
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Install memory in an iMac - Apple Support
Memory Upgrades for Apple iMac 2011 Up to 32GB
OWC Announces 'MaxRAM' Lab Certified Memory Upgrades Up To 16GB For New Mid 2011 Apple iMacs
RAM Upgrade for iMac Mid 2011 21.5-inch | MacRumors Forums
iMac 21.5" Mid 2011 How To Change/Upgrade Your Ram For Better Performance 2014 - YouTube
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com