How to Upgrade Memory in a 27-inch iMac (Late 2012-2013) - YouTube
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
Can you upgrade the RAM in the 27-inch iMac? | iMore
A-Tech 16GB (2x8GB) PC3-12800 DDR3 1600MHz RAM for Apple MacBook Pro (Mid 2012), iMac (Late 2012, Early/Late 2013, Late 2014, Mid 2015), Mac Mini (Late 2012) | 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
2012 21.5-Inch Apple iMac Review: Slim, Sleek, And Stylish, But Far From Shallow | TechCrunch