I recently purchased 2011 21.5 iMac (Mid-2011) and I'm obsessed. : r/mac
A-Tech 32GB (4x8GB) RAM for Apple iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.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
ケーブルの】 Apple - iMac (21.5-inch, Mid 2011)の通販 by Marin's shop|アップルならラクマ タブレット
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
Memory Upgrades for Apple iMac 2011 Up to 32GB
Install memory in an iMac - Apple Support
Memory Upgrades for Apple iMac 2011 Up to 32GB
How to upgrade RAM on iMac 21.5" 2011 - YouTube
Install memory in an iMac - Apple Support
HOW TO: Upgrade The RAM to 32GB on a Mid-2011 21.5inch iMac - YouTube
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET