Apple's 27" iMac Late 2012 model. How to upgrade the ram to 16GB - YouTube
Install memory in an iMac - Apple Support
Apple iMac (Late 2012) review (21.5- and 27-inch) | Macworld
Apple iMac 21.5" Late 2012 Intel Core i5 2.90 GHz 1TB HDD 8GB RAM EMC 2544 A1418 | eBay
CMS 8GB (2X4GB) DDR3 12800 1600MHz Non ECC SODIMM Memory Ram Upgrade Compatible with Apple®
Adamanta 16GB (2x8GB) Apple Memory Upgrade DDR3L 1600MHz SODIMM Compatible for iMac (Mid 2011, Late 2012, Early/Late 2013, Late 2014, Mid 2015), MacBook Pro (Early/Late 2011, Mid 2012), Mac Mini at Amazon.com
Apple Posts iMac (Late 2013) Memory Specifications
Apple iMac Late 2012 21.5-inch 2.7 GHz Core i5 Desktop DDR3 RAM Memory | Kingston
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
APPLE IMAC LATE 2012 27" INCH i7 3.4GHz QUAD 16GB RAM 1 TB HD | eBay