Memory RAM 1x 16GB Apple - iMac Pro 27'' Retina 5K Late 2017 DDR4 2666MHZ ECC REGISTERED DIMM | | RAM MEMORY \ MEMORY FOR APPLE \ APPLE IMAC PRO \ iMac
Install memory in an iMac - Apple Support
iMac Intel 21.5" Retina 4K Display (2017) RAM and SATA Hard Drive Upgrade - iFixit Repair Guide