Memory RAM 1x 4GB Apple - iMac 27'' Mid 2011 DDR3 1333MHz SO-DIMM | MC702G/A 1/2 | RAM MEMORY \ MEMORY FOR APPLE \ APPLE IMAC \ iMac Mid 2011 \ iMac
Adamanta 16GB (2x8GB) Apple Memory Upgrade DDR3L 1600MHz SODIMM Compatible for iMac (Mid 2011, Late 2012, Early/Late 2013, Late 2014, Mid 2015), MacBook Pro (Early/Late 2011, Mid 2012), Mac Mini 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
16GB 2X8GB NEMIX RAM Memory for Apple iMac Mid & Late 2011 at Amazon.com
NEMIX RAM 16GB (2X8GB) DDR3-1333 Memory for Apple iMac 2011 - Newegg.com
Apple iMac 2011 Memory 4GB DDR3 1333MHz PC3-10600 204-Pin
Install memory in an iMac - Apple Support
New 16GB 4x4GB Memory Apple iMac (21.5 and 27-inch, Mid 2011) PC3-10600 at Amazon.com