Crucial RAM 64GB Kit (2x32GB) DDR4 2666 MHz CL19 Memory for Mac CT2K32G4S266M

This went into my 2019 5K 27 iMac (the base model for $1799). It came with 8GB of RAM (2 sticks of 4GB each). I took those out and inserted these two in its place, plus I added 16GB more (2 sticks of 16GB each) in the other slots (also Crucial brand). Everything went perfectly and I now have 48GB of very fast RAM, which should last me 3-4 years (based on my needs/usage). The installation was very quick and easy! I dont know why some reviewers are having such a hard time, its compatible all right! Maybe theyre not seating them in correctly?

Royal pain to install (not the memorys fault), but can confirm that a pair of 16GB single rank work great on my Retina 4K, 21.5-inch, 2017 iMac, not just the 27 they are advertised for, which has the nice little door on the back.

Works perfectly in my iMac 2017, 27 inch, 3.8GHz i5.

100% compatible with 27 2017 iMac

Works just fine on PC too, I knew it would. I am just saying this in case some people were questioning if it would. I bought this instead of regular RAM because it surprisingly was cheaper.

If you have a MAC that allows you to easily swap out the memory RAM like I do, this is the way to go!

I installed this kit (16kb X 2) in iMac/18,3/ 27/i5/3.5kHZ; it took about 5 mins. I placed them in the two empty slots (2&4) and they were recognized immediately. A few days later I switched the new modules with the original ones just to see if there was a difference. I did not use any software to analyze the speed changes if there were any; I could not detect any difference. So, bottom line: new modules are in slots 1&3 (counting from the bottom) and original modules are in slots 2&4 and all is well.

plug and play. Used open dimm slots for the 16gb sticks, did not switch around with existing 8gb (4gbx2) from apple. Performance hit is negligible for my purposes, so not worth the time fiddling. Will be getting another 32gb kit eventually anyway.

worked perfect on 2017 27 iMac

Easy to install following simple instructions. Works just great!