New 21.5-inch iMac least repairable yet due to lack of RAM, hard drive upgradability - 9to5Mac
OWC 8GB (2 x 4GB) PC12800 DDR3L 1600MHz SO-DIMMs Memory Compatible with 2011-2015 iMac, 2011-12 Mac Mini, and 2011-2012 MacBook Pro (Non-Retina Display) Models (OWC1600DDR3S08S) at Amazon.com
Apple iMac 27" 2015 - i5 3.3GHz - 16GB RAM - 2TB HDD - Model Number MK782LL/A - Grade B Used - Walmart.com
How to Install Memory Into a 27-Inch Apple iMac (Late 2015 - 2020) iMac17,1 iMac18,3 iMac19,1 - YouTube