Upgrading a 27-inch iMac 5K to 14 terabytes - Replacing the Fusion Drive with both a SSD and an harddisk
OWC SSD Upgrade Kit For 2010 27-inch iMacs, OWC Mercury Electra 250GB 6G SSD, 18" SATA III 6Gbps data cable, SSD Power Cable, Installation tools and iMac screen adhesive tape set :
27” Mid 2010 iMac Disassembled
hard drive - iMac 27" late 2012 SSD upgrade - Ask Different
iMac Intel 27" EMC 2309 and 2374 Hard Drive Replacement - iFixit Repair Guide
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac