iMac | 2.9 GHz Intel i5 | 21.5 Inch | Late 2013 - Techable.com
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
Apple iMac 27" - Late 2013 Reviews, Pros and Cons | TechSpot
A-Tech 8GB 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
Install memory in an iMac - Apple Support (HK)
Best Buy: Pre-Owned Apple iMac 21.5-inch Desktop "Core i5" 2.9 (Late 2013) 8GB Memory 1TB HDD ME087LL/A