21.5 inch late 2013 iMac - RAM upgrade - Apple Community
How to Upgrade/Install Memory in a 21.5-inch iMac (Late 2012– Mid 2014) iMac14,1 iMac14,3 - YouTube
Configure your own 21.5-inch Apple iMac (2013) at OWC
iMac (21.5-inch, Late 2013) - Technical Specifications
A-Tech 16GB Kit (2x8GB) RAM for Apple MacBook Pro (Mid 2012), iMac (Late 2012, Early/Late 2013, Late 2014, Mid 2015), Mac Mini (Late 2012) | DDR3 1600MHz PC3-12800 SODIMM 204-Pin Memory Upgrade at Amazon.com
Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
Apple iMac 21.5-inch and 27-inch (Late 2013) reviews | Macworld