How to install RAM - Memory on a Apple iMAC 27" 5K - YouTube
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
Memory Upgrades for Apple iMac 2009 - Up to 32GB
How to upgrade the 27-inch 5K iMac (2019) with a massive 128GB of RAM [Video] - 9to5Mac
Install memory in an iMac - Apple Support
Installing RAM into Your iMac >
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)