Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
Install memory in an iMac - Apple Support
What Does It Take To Upgrade a 2012 iMac 21.5"?
How to upgrade a 2012 27" iMac to 24GB of memory - YouTube
How to Upgrade iMac Hard Drive or SSD 2012-2022: EveryMac.com
OWC Announces Memory Upgrades From 8GB to 32GB For 2012 27" Apple iMac
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
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com