Late 2013 iMac review: Faster than before, but the gains over previous models are modest | Macworld
Install memory in an iMac - Apple Support
A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz SODIMM PC3-12800 204-Pin SO-DIMM Max Memory Upgrade at Amazon.com
Apple iMac 21.5-inch and 27-inch (Late 2013) reviews | Macworld