Memory RAM Upgrade for Apple iMac 21.5-inch Mid 2011 4GB/8GB DDR3 SODIMM | eBay
4GB Memory for Apple iMac 21.5-inch (Mid 2011) Core i5/i7 DDR3 PC3-10600 1333MHz SODIMM RAM (PARTS-QUICK Brand) at Amazon.com
A-Tech 4GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010, Mid 2011, Late 2011), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
Apple iMac 27'' 2011 i5 3.1 GHz 4GB RAM 1TB SATA Storage Ref F36 | eBay
A-Tech 4GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010, Mid 2011, Late 2011), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
A-Tech 4GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010, Mid 2011, Late 2011), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
A-Tech 16GB (4x4GB) RAM for Apple iMac (Mid 2010, Mid 2011, Late 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
Apple iMac 21.5" Mid 2011 Intel Core i5 2.7 GHz 1TB SATA Disk 4GB RAM HighSierra | eBay