Memory RAM Upgrade for Apple iMac 21.5-inch Mid 2011 4GB/8GB DDR3 SODIMM | eBay
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
32.0GB OWC Memory Upgrade Kit For 2010-2011 Apple iMac
Memory Upgrades for Apple iMac 2011 Up to 32GB
What to do when your iMac won't turn on?
Memory RAM Upgrade for Apple iMac 21.5-inch Mid 2011 4GB/8GB DDR3 SODIMM | eBay
Install memory in an iMac - Apple Support
I recently purchased 2011 21.5 iMac (Mid-2011) and I'm obsessed. : r/mac
Install memory in an iMac - Apple Support
Apple iMac Mid 2011 21.5-inch 2.7GHz Core i5 Apple DDR3 RAM Memory | Kingston