Timetec Hynix IC 8GB Compatible for Apple 2017 iMac 27-inch w/Retina 5K Display, 2017 iMac 21.5-inch w/Retina 4K or Non-Retina Display DDR4 2400MHz PC4-19200 1Rx8 CL16 SODIMM Memory (Single Rank 8GB) $75 for both