Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
Memory upgrade: Apple iMac 2012/2013/2014 (Howto)
IMAC 21.5" LATE 2012 I5 8GB RAM 1 TB HDD GEFORCE GT 640M MOUNTAIN LION OS T4-C7 | eBay
A-Tech 8GB 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
Install memory in an iMac - Apple Support
Harder, better, faster, stronger: A review of the 27-inch iMac | Ars Technica
Apple's 2012 iMac: Ready for its close-up (pictures) - CNET