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
According to Apple: "iMac (Retina 5K, 27-inch, 2020) DIMMs have a notch on the bottom, slightly left of the middle. If your DIMMs are mixed in capacity, minimize the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4) when possible." From: Install memory in an iMac - Apple Support
Yes, I think that's the best solution: run your iMac with 'only' the two 32GB 2666 MHz modules installed, in slots 1 and 3 (see the diagram that dialabrain posted above). With 64GB of RAM your 2020 iMac will be able to serve you very well.
No need to thank me. Helping others helps me to expand my knowledge too. I live in Europe and can't really come over for a beer or coffee, but appreciate the offer much! :-)
Let us know, if you want, if everything runs fine and at 2666MHz with the 2 x 32GB installed.
Dual Channel functionality? I will explain it in a simple way. Imagine your iMac as being a car with a big engine and lots of power. It will run better and faster if you allow it to use a lot of fuel, which we could compare to the amount of RAM you install. Instead of just installing a fuel tank of a 'normal' size (let's say your current 32GB of RAM), it's possible to install one that is twice as large (your new 64GB of RAM). That's already nice. However, in a non-Dual Channel world, all the 'fuel' needs to find its way to the engine by running through only one tube, one 'channel'. In your Dual Channel car/iMac, there are actually two fuel tanks installed, each with its own 'channel' through which the fuel reaches the engine (the processor). Result: the same amount of 'fuel' (the RAM or Random Access Memory that is 'consumed' or used by the operating system and the applications running) reaches your engine twice as fast in this 'Dual Channel' system as it would in a non-Dual Channel system.
This is also why Apple recommends, in case you install memory modules of different sizes, to minimise the difference in capacity between Channel A (slots 1 and 2) and Channel B (slots 3 and 4). In other words, it is best to have the two 'fuel tanks' as identical in size as possible.
I hope this answers your question about Dual Channel technology. It is a matter of allowing the Intel processor to access the RAM much faster.
I'm pretty sure that if you "only" install the two 32GB modules, one in slot 1 and one in slot 3, your iMac will be more than happy to run your applications very smoothly. That way you avoid having either the memory modules' speed lowered or the Dual Channel functionality disabled.
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.
It is always possible that the two 32GB are defective. I have no first-hand experience with OWC memory modules installed in iMacs. I always use Samsung and never had an issue, not even in combination with the modules installed by Apple. For now, all I can say is that many people using a 2020 iMac and installing third-party memory modules, have problems like yours.
It looks like you have bought these: https://bermuda.desertcart.com/products/127113825-owc-32-0-gb-2666-m-hz-ddr-4-pc-4-21300-so-dimm-260-pin-memory-upgrade-owc-2666-ddr-4-s-32-g-for-2018-mac-mini-macmini-18-1-2019-27-inch-i-mac-i-mac-19-1-and-pc-laptops
If they are, they should be totally compatible. One user commenting on that page, says he had to install the two modules in slots 2 and 4 (and not in 1 and 3) to make things work...
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
