iMac Intel 21,5" Mid 2011 EMC 2428 - used original spareparts for Macs
Open Box Apple iMac 27-Inch Desktop Intel Core i3 3.2GHz, 4 GB Ram, 1 TB Hard Drive - Walmart.com
Install memory in an iMac - Apple Support
Mac RAM Upgrade, Best iMac Memory Upgrade – Best Reviews
How to upgrade RAM on iMac 21.5" 2011 - 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
Install memory in an iMac - Apple Support
32.0GB OWC Memory Upgrade Kit For 2010-2011 Apple iMac
Timetec 16GB KIT(2x8GB) Compatible for Apple DDR3L 1600MHz for Mac Book Pro(Early/Late 2011,Mid 2012), iMac(Mid 2011,Late 2012,Early/Late 2013,Late 2014,Mid 2015), Mac Mini(Mid 2011,Late 2012) MAC RAM at Amazon.com