iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
iMac 27-Inch "Core i7" 3.5 Late 2013 Max RAM is higher than 32gb | MacRumors Forums
A-Tech 16GB Kit (2x8GB) RAM for Apple MacBook Pro (Mid 2012), iMac (Late 2012, Early/Late 2013, Late 2014, Mid 2015), Mac Mini (Late 2012) | DDR3 1600MHz PC3-12800 SODIMM 204-Pin Memory Upgrade at Amazon.com
Apple Posts iMac (Late 2013) Memory Specifications
SSD Upgrades for Apple iMac 27-Inch Late 2013 - 2019
Install memory in an iMac - Apple Support
Apple iMac 21.5-inch and 27-inch (Late 2013) reviews | Macworld
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)