2011 iMac, 21.5-Inch Screen | Free Shipping Available
Install memory in an iMac - Apple Support
I recently purchased 2011 21.5 iMac (Mid-2011) and I'm obsessed. : r/mac
OFFTEK 2GB Replacement Memory RAM Upgrade for Apple iMac 2.5GHz Intel Quad-Core i5 - (21.5-Inch) (DDR3 - Mid 2011) (DDR3-10600) Desktop Memory at Amazon.com
Memory Upgrades for Apple iMac 2011 Up to 32GB
iMac Mid 2011 21.5" Upgrade Kit - Real Mac Mods
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
Apple iMac 21.5-inch | Extended Warranties & Free Shipping
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET