Upgrading RAM on Late 2015 iMac, has 4 slots, installed 4x8GB of new memory bars, no go, take top one out, install 4GB and all works, tested each 8GB bars, all working, they are all well seated in each slot, why is the iMac not accepting a full 32GB of memory as specified it will?
What model? 21"? 27"? 5K?
Only the 27" Retina 5K iMac from 2015 can use more than 16GB of RAM.
lets start with basics, where did you purchase the RAM ? The reason I ask is iMacs are fussy about using high quality RAM. If you bought a value RAM that may be the issue.
What company manufactured the RAM?
What is the listed speed of the RAM?
How do you know the RAM is working?
the original RAM work fine, 2x4GB bars, I removed those and replaced with 2x8GB OWC a couple years ago, did not put the original RAM back (stupid thing to do) late last year I added 2x8GB of third party RAM from OWC, so I now had 32GB of third party OWC Ram in, but, it wouldn't boot. So I took one of the 8GB out, then it booted, then I reconfigured that ram in different slots, booted fine, I swapped the extra bar out with the 3 bar configuration and it worked too, so I thought that one of the slots must not be working... until I put 1x4GB bar into that slot, then it booted also, so that didn't seem to make the slot not working for me. got to be something to do with this iMac not being able to handle 32GB as it says, currently running 28GB (1x4GB, 3x8GB) all the 8GB bars are third party from OWC. Not sure if I can make it any clearer, would there be a setting or adjustment limiting the Ram amount?
just did a little more testing on these new 8gb bars, now the one I had in there is not working, so they're both buggy I would say. So Buster, even though these are set up to take 32gb, how can you put more in and have it working, I thought the max was 32?? by the way I appreciate your help here. tks
OWC is manufacturer
Memory 1867 MHz DDR3
the ram is working, tried diff configs, they all work... even the original 4GB bars
iMac 27" 5K Retina, 4 GHz intel Core i7
Late 2015
FWIW, it's not because it can't use 32GB. I have a Late 2015 5K iMac and it works fine. It can actually use 64GB. Don't know what is wrong with yours.
What is FWIW
Sorry wrong guy!! for all the hassle maybe they'll swap me out with some 16GB instead of the 8's that don't work,
tks for you help again.
Welcome
Looking at this logically:
I would still like to know how you *know* the third-party RAM works, when clearly, by your own admission, it does not work when it is the only RAM in your iMac. If your Mac works with the RAM that shipped with it, and does not when when you remove that RAM, the troubleshooting is over.
iMac won't take full 32GB Ram...
