Apple Classifies Early 2013 21.5-inch iMac as Obsolete - MacRumors
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How to Upgrade RAM on MacBook Pro, iMac & More | AVG
How to Upgrade/Install Memory in a 21.5-inch iMac (Late 2012– Mid 2014) iMac14,1 iMac14,3 - YouTube
21.5 inch late 2013 iMac - RAM upgrade - Apple Community