Apple iMac 21.5" Retina 4K - Mid 2017 Reviews, Pros and Cons | TechSpot
Teardown of New 4K 21.5-inch iMac Reveals Removable RAM and Modular CPU - MacRumors
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
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
Apple 21.5" iMac with Retina 4K Display (Mid 2017) MNDY2LL/A B&H
The New 2017 iMac: Notes & Tidbits on RAM - The Mac Observer