Review on Timetec 32GB RAM Upgrade Kit for Apple 2017 iMac: Boost Performance with DDR4 2400MHz PC4-19200 SODIMM MAC RAM by Brennan Buckley

If you're buying a 27" iMac, don't worry about Apple's expensive memory upgrade options. With this Timetec memory kit, you get twice the storage (32GB vs. 16GB) for a few dollars compared to Apple's price. They're also cheaper than Mac-focused stores and providers. The memory slots directly into the slots above the power connector (make sure you align the tabs correctly). Once enabled, you'll see fewer disk writes and smoother performance. One thing that isn't obvious is that you can keep the existing 2 x 4GB modules, leaving you with 40GB of RAM to play with. The purchase is definitely worth it.