NEMIX RAM 16GB Kit (2x8GB Upgrade) DDR3-1600 SODIMM PC3-12800 for Apple MacBook Pro Mid 2012 / iMac Late 2012 / iMac 2013, Late 2014, Mid 2015, Mac Mini Late 2012 at Amazon.com
Teardown of new 21.5-inch iMac surprisingly reveals user-upgradable RAM, modular CPU - 9to5Mac
Apple Officially Confirms 21.5” iMac RAM Is Non-User-Replaceable
21.5" iMac Has No User-Upgradable RAM; 27" Has Four Accessible RAM Slots - MacRumors
Install memory in an iMac - Apple Support
How to Upgrade iMac RAM: 2012-2022: EveryMac.com
Memory upgrade: Apple iMac 2012/2013/2014 (Howto)
How to upgrade RAM iMac late 2013 21.5inch - break & fix MOVIE - YouTube
16GB -2x8GB Memory Ram Upgrade 21.5" Apple iMac-13.1 Core i3 3.3GHz Early 2013 | eBay