iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
CMS 32GB (4X8GB) DDR3 12800 1600MHz Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core I5 3.2 27-Inch (Late 2013) Me088Ll/A - A6 at Amazon.com
A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz PC3-12800 SODIMM 204-Pin Memory Upgrade at Amazon.com
Memory upgrade: Apple iMac 2012/2013/2014 (Howto)
2013 iMac teardowns reveal SSD slots, soldered-in CPU in the 21.5” model | Ars Technica
Timetec Hynix IC 4GB Compatible for Apple DDR3L 1600MHz PC3L-12800 SODIMM Memory Upgrade for Early/Mid/Late 2011, Mid/Late 2012, Early/Late 2013, Late 2014, Mid 2015 MacBook Pro, iMac, Mac Mini (4GB) Laptop Memory -