How to Upgrade Memory in a 21.5-inch or 27-inch iMac (Mid 2010) - YouTube
A-Tech for Apple 16GB Memory Ram Kit 2X 8GB PC3-12800 1600MHz MacBook Pro 13-inch/15-inch Mid 2012 iMac 21.5 inch Late 2012 Early Late 2013 Late 2014 Mid 2015 Mac Mini Late 2012
8GB Memory (PC3L-12800, DDR3L 1600MHz) for Apple MacBook Pro 15 inch A1286 Mid 2012. Apple MacBook Pro 13 inch A1278 - Mid 2012. iMac 21.5 inch A1418 Late 2012, A1418 Early 2013,
Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
Install memory in an iMac - Apple Support
Apple iMac Late 2012 21.5-inch 2.7 GHz Core i5 Apple DDR3 RAM Memory | Kingston