Apple 27-inch iMac with Retina 5K display (2017) review: All-in
Install memory in an iMac - Apple Support
2017 5K iMac Review - Faster, Lower Price, and an Amazing display! - YouTube
iMac Retina 5K: Memory upgrade (RAM)
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
How to upgrade the 27-inch 5K iMac (2019) with a massive 128GB of RAM [Video] - 9to5Mac
Micron MT8KTF51264HZ-1G6E2 8GB (2 x 4GB kit) OEM RAM Memory for Apple iMac Retina 5K 27 inch (Late 2014) Core i5 / i7 PC3-12800 DDR3-1600MHz 204-Pin SoDimm
Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else
A-Tech 64GB (4x16GB) RAM for Apple iMac 2017 27 inch Retina 5K | DDR4 2400MHz SODIMM PC4-19200 2Rx8 1.2V 260-Pin SO-DIMM Memory Upgrade Kit at Amazon.com
The New 2017 iMac: Notes & Tidbits on RAM - The Mac Observer