iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
HOW TO: Upgrade The RAM to 32GB on a Mid-2011 21.5inch iMac - 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.... | eBay