iMac Intel 21,5" Mid 2011 EMC 2428 - used original spareparts for Macs
How to upgrade RAM on iMac 21.5" 2011 - YouTube
NEMIX RAM 32GB (4x8GB Upgrade) DDR3-1333 PC3-10600 204-Pin SODIMM Memory for Apple MacBook Pro Early/Late 2011, iMac Mid 2010 27 inch 4-Core, iMac Mid 2011 21.5/27” , Mac Mini Mid 2011 at Amazon.com
A-Tech 32GB (4x8GB) RAM for Apple iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
Apple iMac 21.5-inch Mid 2011 2.5GHz Intel Core i5 (MC309LL/A) – UNICOM, Inc.
HOW TO: Upgrade The RAM to 32GB on a Mid-2011 21.5inch iMac - YouTube