A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz SODIMM PC3-12800 204-Pin SO-DIMM Max Memory Upgrade at Amazon.com
Memory upgrade: Apple iMac 2012/2013/2014 (Howto)
What Does It Take To Upgrade a 2012 iMac 21.5"?
Refurbished: Apple iMac 21.5-Inch "Core i5" 2.9GHz (Late 2012) A1418 MD094LL/A 8GB RAM 1TB HDD NVIDIA GT 650M MacOS MOJAVE USB Keyboard & Mouse Grade B - Newegg.com
Harder, better, faster, stronger: A review of the 27-inch iMac | Ars Technica