iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
I recently purchased 2011 21.5 iMac (Mid-2011) and I'm obsessed. : r/mac
Install memory in an iMac - Apple Support
i5 LED iMac (21.5-inch, Mid 2011)
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
A-Tech 8GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
32.0GB OWC Memory Upgrade Kit For 2010-2011 Apple iMac