How to Install an SSD Card into a 21.5-inch iMac (Late 2012–Early 2013) iMac13,1 - YouTube
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SSD Upgrades for Apple iMac 27-Inch Late 2013 - 2019
Hard Lesson Learned With Late-2013 Apple Products Containing Lesser Performing 128GB SSDs | The SSD Review
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Amazon.com: OWC 2TB Aura Pro X2 NVMe SSD Upgrade Kit Compatible with Select 27" and 21.5" iMac Models (Late 2013 - Current) : Electronics
Amazon.com: INDMEM NVMe PCIe SSD 256GB 3D TLC NAND Flash Hard Drive Replacement for Mid 2013-2017 MacBook Air, Late 2013 - Mid 2015 MacBook Pro Retina, Late 2013-2017 iMac, 2013 Mac Pro, 2014 Mac Mini : Electronics