RAM for new iMac

Hi all - lots of people here WAY more knowledgeable than I am on Mac hardware so I have a question. I purchased a new iMac 2020. It came with 8 GB RAM. I have 2 options to install my own

  1. 4 8GB sticks and remove apples Ram and save it
  2. 2 16GB sticks and mix them with Apples Ram for a total of 40… but they’d be mismatched.
  3. Just the 2 16GB new sticks for the same as option 1

Is one technically better than the other (besides the obvious 8GB more RAM in option 2 :slight_smile: )

I’ve heard differing views on mixing RAM and quad vs dual etc… or having all 4 slots filled is better than 2 open. Or am I just sweating the details ?


Don’t worry about mismatching - it’s not an issue with real-world consequences. I have that 40Gb option in my 2017 Retina iMac (bought this RAM or roughly twice what it’s going for today) and it’s perfectly fine.

Get RAM from Crucial (either directly from them or from Amazon) or from OWC/macsales.com

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Thanks for the quick reply ! Do to a mix up in shipping i have both RAM packages ! So I will go with the 2 16GB and 2 8 GB from Apple

One thing I was worried about when making my purchase was reading some people (probably macrumors forum and/or Reddit) saying that their systems wouldn’t restart after adding RAM, or that the system froze. The issue for them was solved, if I remember right, by re-seating the RAM in some different placement. But luckily for me I just followed Crucial’s basic instructions and never had a problem.

OWC usually posts instructional videos, even for super-easy things like adding RAM to a 27-inch iMac, which takes maybe two minutes. I don’t see a video for the 2020 iMac, but I doubt it’s any different than the procedure for older models - video here:

Well - its up and running! I opted for the 2 32 GB sticks and the 2 Original from Apple - so it’s 40 GB, but mismatched :wink: But all seems good so far! I will keep an eye on the system - another side benefit is that I won’t lose the origami Apple Ram now :slight_smile: With the other option I had to store the 2 Apple Sticks someplace…

by the way, I stored them in this configuration:

One of the videos suggested to put the 4 GB sticks in the first two slots and the new sticks in the bottom two slots. Is that correct?? I dont now about pairing etc…

Thanks again for the help !

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The RAM should be installed in alternating slots in the back of the iMac so that each ‘pair’ is associated with the same DIMM (which is contrary to the numbering of the BANK slots)… It’s kind of confusing, I’m not sure why the numbering conventions are opposite…

So, you want to just switch the positions of the two “middle” sticks.

The correct configuration will show up like this in the “About This Mac” and “System Information” (in the Memory tab) windows:

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That was my assumption too… and i was confused by the video -unless as you’re saying, I understood wrong ? It seems to be working … should I still change it ?

Here’s the video: https://9to5mac.com/2020/08/09/how-to-upgrade-2020-imac-ram-video-5k-27-inch-128-gb/

They mention that the 2020 iMac is unique and they get better performance the way i did it
QUOTE “ Instead, I found that it’s best to install two like modules in slot 1 and 2, and the other two like modules in slot 3 and 4 for the best performance. Notice how the same memory configured in this arrangements results in the proper 2666MHz (2667) speed rating. Be sure to watch the video walkthrough above for more details”

What do you all think. This group has folks way smarter than me in this stuff !


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His results don’t make any sense from my experience with many computers. But I don’t have the 2020. My 2019 runs with memory at full speed with modules installed “normally”. Click on Overview–>System Report to see what is installed. Try swapping and see if there is a speed loss.

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Honestly?? Im scared :slight_smile: - Its working ! I think I’ll keep an eye on it…

Screen Shot 2020-08-11 at 6.31.39 PM|690x306

Hmm… this is interesting. When I get my new 2020 iMac I’m going to have 4x of the same sticks in it so I won’t have to worry, but I will be following this / looking into it…

Yes, thank you and please keep me posted. I am keeping it the way it is for now (same as the pic I posted above) and I will keep an eye on it. But all is working well

It works but there might be a performance hit. Just because the memory runs full speed doesn’t mean the system will. Try running GeekBench with both RAM configurations and report back here.

I hope @Zack can do this. This is out of my comfort level :slight_smile: But you have me curious. I hope someone on the link I posted from 9to5mac tests this too

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So, I decided to try part of the experiment. I don’t know much about geekbench so I didn’t use that. But I swapped the RAM as suggested - alternating the OWC 16 GB sticks with Apples 4 GB sticks and the results showed 2133 (I think, I don’t remember the exact number). When I put them back to my way - Apple 4GB sticks in slot 1 and 2 and the OWC in 3 and 4 … it showed the 2667.

Lots of good info in this thread here…https://forums.macrumors.com/threads/memory-upgrade-troubleshooting-in-2020-27-inch-imacs.2249254/… but mostly above my head :slight_smile: I think they are coming to the same conclusion at @tomalmy and that overall Geekbench scores will be lower putting in RAM the 9to5 Mac way (the way I did above) even though it shows 2667… Interesting !

Yep. See posts 15, 20, and 33-34 for people running Geekbench with both stick orders. The 9to5mac order was slower in all cases.

Thanks @tomalmy… your hunch was right! So what do you suggest for me?

The 2x16 OWC sticks in slots 2 and 4, leaving 1 and 3 empty; or add the apple 2x4GB sticks to 1 and 3?

Sorry, was away “on business” and didn’t get a chance to swap my sticks to run Geekbench – good thing that you found that link.

From top to bottom:
Slot 1: 4GB
Slot 2: 16GB
Slot 3: 4GB
Slot 4: 16GB

When you first opened the door to change the memory, Apple’s sticks should have been installed in Slots 1 and 3, and you just put the additional sticks in 2 and 4 and close it back up.

My new iMac will be here on the 20th but I will have four matching sticks of RAM so my order won’t matter…

You should download Geekbench 4 (it’s free) and run it before you change, and then after you change, so you have your own information. Geekbench 5 doesn’t have detail memory bandwith information like Geekbench 4 does, so don’t use that one for this.

Let us know how it goes!

Add the memory. 40 > 32. or another way, 8 > 0.