Apple iMac Retina 4K 21 .5 inch Late 2015 2.8GHz i5 16GB RAM 1.02 Fusión drive | eBay
OWC 32GB (4 x 8GB) PC14900 DDR3 1866MHz SO-DIMMs Memory Compatible with 2015 (Late) iMac 27" w/Retina 5K Models and Compatible PCs (OWC1867DDR3S32S) at Amazon.com
OWC 8GB (2 x 4GB) PC12800 DDR3L 1600MHz SO-DIMMs Memory Compatible with 2011-2015 iMac, 2011-12 Mac Mini, and 2011-2012 MacBook Pro (Non-Retina Display) Models (OWC1600DDR3S08S) at Amazon.com
Apple's 4K 21.5-Inch iMac Allows You to Upgrade RAM and CPU – Company Finally Dialing Down on Soldered Components, Reveals Teardown
5K iMac (Late 2015) RAM Upgrade - YouTube
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