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How to Upgrade iMac RAM: 2012-2022: EveryMac.com
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
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16GB Memory Upgrade Kit for 2012-2013 iMac 21.5-Inch
NEMIX RAM 16GB Kit (2x8GB Upgrade) DDR3-1600 SODIMM PC3-12800 for Apple MacBook Pro Mid 2012 / iMac Late 2012 / iMac 2013, Late 2014, Mid 2015, Mac Mini Late 2012 at Amazon.com