Apple iMac (21.5-inch, late 2013)2.7GHz Quad-core Intel Core i5 8GB RAM 1TB HDD | eBay
21.5 inch late 2013 iMac - RAM upgrade - Apple Community
Apple iMac 21.5" Late 2013 Core i5 2.7GHz 8GB RAM 1TB HDD MacOS Big Sur 11.5.7 | eBay
Memory upgrade: Apple iMac 2012/2013/2014 (Howto)
Apple iMac 21.5-Inch (Late 2013) "Core i5" 8GB RAM 1TB HDD Intel Iris Pro | eBay
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
iMac (21.5-inch, Late 2013) - Technical Specifications
Apple iMac review (2013) | Engadget
Performance - Apple 21-inch iMac, late 2013 review | TechRadar
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
Apple iMac 21.5-inch 2.7GHz Quad-core i5 (Late 2013) | mac of all trades