I have a 2020 iMac. I am running two 16GB each in its own slot. I just bought two 32GB to add to the RAM. I have read both ways to install: put the 16s in slots 1 and 3 and the 32s in slot 2 and 4. I have also read that it doesn't matter how they are installed. That I could put one set in 1 and 2 and the other in 3 and 4. Please let me know which is correct. All four run at 2666. Thanks for any help anyone can provide.
iMac 27″, macOS 12.6
I disagree!
Minimising the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4) means that the capacity in GB of the memory modules to be installed in Channel A should match as closely as possible the capacity in GB of the memory modules to be installed in Channel B! If you would put the 16GB modules in slot 1 and 2 or in slot 3 and 4, you would actually do the opposite of what is recommended, i.e. you would be increasing the capacity difference between Channel A and B: 32GB in one channel versus 64GB in the other one...
In other words and in this case, and looking at the image in the reply above:
Because slots 1 + 2 make up Channel A and slots 3 + 4 Channel B, in this case both Channels have the same amount of RAM at their disposal (in this case, each channel has 48GB), which is exactly what Apple recommends by saying "minimise the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4). Also, I recommend putting the highest capacity memory modules (in this case the 32GB modules) in slots 1 and 3.
After installation of the memory modules, you can check if you did the right thing in the "Hardware > Memory" section of System Information (you find that application inside the Utilities folder on your iMac). I add a screen capture of my memory banks's layout to help you understand better (look at "Channel A" and "Channel B": the same amount of memory). Also know that Bank 0 equals Slot 1, Bank 1 = Slot 2, etc. In my case each Channel has 20GB at its disposal.
I just put them back in the correct order and it is still showing 2133MHz. I have been unable to do a screenshot and I don't know why. I will copy all the info from the package of the 32GB modules. I do have a photo of that but I don't know how to get it to you. I will shut down my iMac now and put the info on my other computer.
Thanks for your patience.
I bought the machine brand new in Spring 2021. It came with 16GB RAM and I bought two 16GB modules and replaced the two 8GB modules that came with the computer. What I didn't do was just add the two 16GB modules to the existing two 8GB modules. I am going to take out the 32s that I just bought and see if the speed goes up to 2666MHz. But I need a break today, this is stressing me out. Thanks foryour help. I'll be in touch tomorrow?
I will take your suggestion and run with it, install the new 32GB modules. I am not educated in "dual channel functionality" so if you could please explain that I would like to know about it. Sadly for me at this point I have spent almost as much for RAM as I could have had installed when the machine was ordered from Apple. Well maybe not that much. Anyhow, I don't know how to thank you enough for all the work and time you have put in to help me in this mess. If you lived close to the west coast of Florida I'd buy you a beer or coffee. Many thanks.
I did install the modules correctly. I have made sure they clicked when I put them in. No luck. So I called a local iMac expert and he told me to reinstall the 16GB one at a time. I did that and now am back to where I was before I ordered the 32GB modules. The machine came on as it is supposed to. My suspicion is that the 32GB modules are defective. The brand of the 32s is OWC but I am unable to find most of what you asked for. I see that it is 2666DDR4 and immediately following that is S32G. There is no other identification on the modules. I am sending them back to OWC. And I just checked and the machine is running 2667MHz. I'll let you know the outcome of my return to OWC if you are interested.
Regards and thanks.
I called OWC and I will be returning the modules. I have Crucial RAM in there now and I intend to buy Crucial to replace these OWC modules. I'll keep you posted when I get the Crucial and try that. I did buy the modules as you described above.
Cheers
I can't thank you enough for taking the time to help me. Now I can install them with no worries. I hope you have a Happy New Year. Cheers, Dick B,
[Personal Information Edited by Moderator]
You're most welcome. Enjoy 2023.
Thank you very much for the clarification. I have not yet installed the new RAM and now will be able to do it correctly. Happy New Year.
What are the specs of the 32GB modules? 2133 or 2666MHz?
They are 2666Mhz
Strange. A couple questions. Did you buy the iMac new or refurbished? Did the 16GB modules come with the Mac or did you add them?
You're welcome. You should probably check the speed with just the 16GB modules and just the 32GB modules. Try not to stress over it. Things happen.
So I just installed the two 32GB modules. When I hit the button on the back of the machine nothing happened. It is not coming on. Any suggestions?
Adding RAM
