iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
Hynix IC 32GB KIT4x8GB Compatible for Apple DDR3 1333MHz PC310600 for iMac Mid 2010 27 inch Mid 2011 21527 inch MAC SODIMM Upgrade | MAX RAM Upgrade for iMac 113 iMac 121 iMac 12 2 - Newegg.com
Install memory in an iMac - Apple Support
How to Upgrade the RAM in Your iMac
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com