iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
Is it worth it to upgrade RAM on Mid 2010 21.5 iMac? | MacRumors Forums
Timetec Hynix IC 4GB Compatible for Apple DDR3 1333MHz PC3-10600 for MacBook Pro (Early/Late 2011 13/15/17 inch), iMac (Mid 2010, Mid/Late 2011 21.5/27 inch), Mac Mini(Mid 2011) MAC SODIMM RAM Upgrade- Buy
How to Prepare Your Mac for macOS High Sierra - The Mac Security Blog
How to Upgrade the Memory in the Late 2017 iMac Pro