Adamanta 32GB Memory Upgrade Compatible for 2017 Apple iMac 27" Retina 5K Display DDR4 2400Mhz PC4-19200 SODIMM 2Rx8 CL17 1.2v Dual Rank RAM DRAM

EDIT: I just benchmarked the differences between my original 8GB VS New 32GB VS 40GB Combined. Running the iMac on just the new 32GB Adamanta RAM got the best results. (Photo of results provided) I did test on Geekbench and Novabench and the results were the same. 7-8% overall performance improvement compared to having the 40GB and even better than having the original 8GB. Where I noticed the most difference was in the responsiveness of the programs, cpu performance and also in the read and write speeds on the Fusion Drive. Huge memory performance boost by using the full utilization of the dual channel memory as opposed to dual channel asymmetric (which is technically single channel apparently) when you mix the modules. The best scenario would be to go for the full 64GB of this memory. I'm very pleased with 32GB however and not at all sweating missing out on the extra 8GB. I'll just sell them.

Original Post:
I had a similar problem as others with the iMac not starting... Read more

My 2 x 16Gb modules arrived today.
I'm writing this because many will probably make the same mistake that I did.
I removed the 2 x 4Gb modules that came with the machine and inserted the 2 X 16Gb Adamata modules in the slots they had occupied. I then took the original 2 x 4Gb modules and inserted them into the 2 remaining slots, replaced the cover and tried to power it up. Nothing but a black screen. Let's fast forward to the solution. Insert the 2 x 16Gb modules into the 2 top banks as they are bank 0 while the 2 lower ones are bank 1. If you choose to insert your original Apple 2 x 4Gb modules into the 2 lower slots and then power up. Don't be surprised if it takes a few seconds before you see anything happen, Adamanta customer support (which by the way was outstanding for me) says this is normal the first time booting after new memory is installed.
iMac should boot fine with modules installed as described above and in the picture.
Love my 2017 iMac 27"... Read more

This might be my first Amazon review after many purchases to support Amazon's $136 billion dollar in sales last year. Ha, anyways I recently purchased a 2017 iMac from Apple. My wife has a photography and videography business and she needed a superior computer to our 2015 iMac. After much research from a non-computer guy, I decided against buying extra RAM through Apple and getting a 32gb set up from Adamanta. Install seemed easy from my research and come to find out, it is an easy install. I did have trouble with the new iMac not powering on after I installed the new RAM. I took out the newly purchased RAM, started it up and set up the new iMac. After set up, I shut it down and tried installing them again with no luck. I called Adamanta technical support and they told me to take out both 4gb Apple RAM and put the new 32 gb RAM in the top two slots. The original Apple RAM was in slot #2 and #4. I left the Apple RAM out and it powered up with the new RAM installed. I then shut it down... Read more