RAM Upgrade for iMac Mid 2011 21.5-inch | MacRumors Forums
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
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
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
How to upgrade RAM on iMac 21.5" 2011 - YouTube
Install memory in an iMac - Apple Support
Apple iMac 2011 21.5” Intel i5 2.7 GHz 8GB RAM 1TB HD AMD 512 MB, Office, I Life | eBay
Memory Upgrades for Apple iMac 2011 Up to 32GB
2011 Apple iMac 27" Intel i5 2.7GHz 8GB RAM 512GB SSD AMD Radeon HD 6770M | eBay