Apple's 2012 iMac: Ready for its close-up (pictures) - CNET
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
Install memory in an iMac - Apple Support
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
Install memory in an iMac - Apple Support
iMac RAM Upgrade mixing different memory sticks: 27” iMac late 2013 - YouTube
2013 iMac teardowns reveal SSD slots, soldered-in CPU in the 21.5” model | Ars Technica