Apple's 27" iMac Late 2012 model. How to upgrade the ram to 16GB - YouTube
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
Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
The Case of the Late-2012 iMacs - MacStories
iMac Intel 21.5" EMC 2544 Teardown - iFixit
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)