How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
Memory Upgrades for Apple iMac 2011 Up to 32GB
How to upgrade RAM / Memory on a 2010 iMac Core i3 i5 i7 (21.5in & 27in) - YouTube
install - Installing and Upgrading Ram on a mid 2011 iMac (different size RAM) - Ask Different
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
iMac 21.5" Mid 2011 How To Change/Upgrade Your Ram For Better Performance 2014 - YouTube
How-To: Boost your Mac's speed and prolong its useful life with easy RAM upgrades - 9to5Mac
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
Shop Imac Mid 2011 Memory Upgrade | UP TO 59% OFF
How to Improve Multitasking with an iMac Ram Upgrade?
OWC 2.0GB PC10600 DDR3 1333MHz SO-DIMM Compatible with 2011 MacBook Pro, Mid 2010/2011 21.5" & 27" iMac Models, 2011 Mac Mini (OWC1333DDR3S2GB) at Amazon.com
Install memory in an iMac - Apple Support
OFFTEK 4GB Replacement Memory RAM Upgrade for Apple iMac 2.5GHz Intel Quad-Core i5 - (21.5-Inch) (DDR3 - Mid 2011) (DDR3-10600) Desktop Memory at Amazon.com
A-Tech 16GB (4x4GB) RAM for Apple iMac (Mid 2010, Mid 2011, Late 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com