Replacing late 2015 27" iMac flash drive | MacRumors Forums
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iMac 27" Late 2015 A1419 4K - SLOW Fusion hard drive replacement with new internal SSD, MUCH FASTER! - YouTube
Timetec 256GB MAC SSD NVMe PCIe Gen3x4 3D NAND TLC Internal SSD Compatible with Apple MacBook Air (2013-2015, 2017), MacBook Pro (2013-2015), iMac (2013-2019), Mac Pro (2013), Mac Mini (2014) - Walmart.com
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac