iMac 21.5" Mid 2011 How To Change/Upgrade Your Ram For Better Performance 2014 - YouTube
Install memory in an iMac - Apple Support
21.5” mid-2011 iMac wires? Finally trying to upgrade my RAM and these wires are blocking the slot — did get an iMac with poor build quality? What can I do? : r/mac
Timetec 16GB KIT(4x4GB) Compatible for Apple DDR3 1067MHz / 1066MHz PC3-8500 CL7 Dual Rank for iMac (Late 2009 21.5-inch / 27-inch) SODIMM Memory MAC RAM Upgrade for iMac 10,1 and iMac 11,1 at Amazon.com
The New 2017 iMac: Notes & Tidbits on RAM - The Mac Observer