OWC 16GB (2 x 8GB) PC19200 DDR4 2400MHz 260pin SO-DIMMs Memory Ram Upgrade Compatible with 27" iMac w/Retina 5K (Mid 2017) and Compatible PCs (OWC2400DDR4S16P)

Great price on a great product. iMac recognized the modules and everything works wonderfully. Highly recommended.

I have a mid-2017 iMac 27 inch Retina with the 4.2 GHz Intel i7 with 2TB Fusion DriveINITIAL PROBLEMS (All Resolved):FiIRST PROBLEM: Replacing the 32gb memory with 64gb, the Mac initially didn't boot.I had to put my old memory back, boot it up, then try different configurations where I would keep original 16gb memory and place new 32gb making a total of 48gb. First time didn't work. Put the two sticks aside, and put the other two sticks in. Success! I now had 48gb. But, the system was slow as snot and took a long time after logging in. Now, I shut it down, removed original memory and moved 32gb upgraded memory to position 1 and 2 and put the sticks that weren't working in position 3 and 4. Finally, booted up! 64gb memory!SECOND PROBLEM: As mentioned everything was slow. I now had 64gb memory, but everything was slow but not as slow. Once I had mouse movement, I immediately removed the cache files in the library folder. Then I started opening up the apps that I use the most, first. With Fusion Drive, it uses a large cache to make opening apps a lot faster. The Fusion Drive is a mix of Flash or SSD and HDD. After using it for 4 hours and rebooting once everything became quite snappy and by the second day, I can finally see the payoff of having 64gb of memory.I have experienced issues with memory not allowing computer to boot up before, even in Windows. Sometimes memory sticks just have to be put in a specific order and no one knows that until they try. Most of the time, no issue.The GOODSo far, I am no longer needing a swap file. The responsiveness of apps and loading data is noticeably faster. This is a cheap upgrade that adds immediate benefits and well worth the money. More memory gives the system more headroom to work with.I was considering buying an M4 MacMini to replace this 2017 iMac because I felt it was important to have the speed and memory to tackle whatever tasks I need to plow through. Adding the memory changed that decision and helped to extend the life of this machine for another few years. I would rather save the money and use what I have.If you are on the fence, just do the upgrade. You will notice a difference and it will give your Mac new life. I only feel bad that I didn't make this choice years ago, or when I first bought the Mac. Of course, back then, the cost was double than what it is now.

Works without a hitch in a Thinkpad T580 bought used with minimal 2018 specs. Now can have near infinite browser tabs, multiple programs, and processes with little fuss. 64gB a bit of overkill for Linux, but the Windows appreciate the extra room.

Worked just as advertised ...

OWC 32GB (2 x 16GB) 2400MHZ DDR4 SO-DIMM PC4-19200 Memory Upgrade For 2017 iMac 27 inch with Retina 5K displayI recently bought an iMac 2017 27" 5K retina base model with 8Gb RAM and wanted to add some RAM. After investigating for 32 Gb RAM for iMac 2017 27" from well known brands, I decided to go with OWC. It was a risky process for me because it was an International shipment for me and if something goes wrong returning it would be a hard process and the disappointment would be much higher. The package was scheduled to arrive between 2-12 April 2018 but to my surprise it was delivered to me on March 26th :) I fitted the RAMs in excitement (despite having dealing with hardware for years, I took my time to read and watch OWC and Apple advice first). My process was exactly like this:-Shut down and wait for about 10 mins (I wouldn't but it wouldn't harm I thought).-Placed the iMac on a soft cloth and opened the RAM bay.-Preinstalled 8 Gb RAM was on slots 1 and 3.-Insatlled OWC 16 Gb modules on slots 2 and 4.-Closed the bay, plugged the cables and turned it on.Voila, after 15-20 seconds apple logo was on screen and it booted without no problems. Checking RAM it shows a botal of 40Gb now.Thanks OWC. Wish you had an office in my country or at least I could buy anything from you internationally.After using these RAMs for months, I decided to buy another 32 Gb and upgrade to a total of 64 Gb. Removed the stock 8 Gb and placed the new 32 Gb set. Now working with 64 Gb. :) All went well (bought second set from Newer Galaxy Distribution Company, LLC through Amazon - delivered just on time. Thanks)