The 9to5 method worked to restore the speed to 2667 MHz, but I believe that they would have lost dual channel using that arrangement. So everything would have looked fine in System Report, but the memory would have been functioning in a sub-optimal way. I don't remember them actually testing that in the video, so I wouldn't want to say one way or another. But this seems to be what's happened to a few of us on this thread when we try to pair Apple OEM RAM with compatible after market RAM.
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Memory upgrade troubleshooting in 2020 27-inch iMacs
- Thread starter KrazyKanuck
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Yes you’re right it would appear it would lose dual channel with the 9to5 Mac method since the memory won’t be paired.
How do recommend i try this ? Use Geekbench and if so what values to compare the before and after memory upgrade? Cheers
What configuration did you order? I would run Geekbench with the stock RAM configuration. Run it again with your new RAM and Apple's OEM RAM, but make sure that you have the new RAM in one DIMM and the OEM in another. And then run it again with just your new RAM in place of Apple's OEM RAM. Apologies if this is old news to you, but just make sure that Finder isn't indexing files or that other processes are running in the background when you're running Geekbench.
Here are some Geekbench scores for iMac20,1:
And here are some for iMac20,2:
I'm not sure whey there are to different models. I think this is the first year that the 27-inch iMacs have two different model identifiers. Maybe its the nano glass, maybe it's the additional storage module in the higher capacity BTOs. You can look through these to get an idea of what you should be scoring (you can click on the link in each score to view system details). Having more than 32GB of RAM doesn't seem to make a noticeable difference in these scores.
I have the same issue after getting my new 2020 iMac today, same Crucial RAM (CT2K8G4S266M). Sounds like we have a few options.
1) Run 16-16-4-4 and lose dual channel.
2) Run in dual channel but at 2133 MHz
3) Run just 2 sticks of aftermarket at 2666 MHz
I'm leaning towards option 2. I'd rather have the extra 8GB memory at the slower speed, I'm not sure I will notice any difference in actual usage.
1) Run 16-16-4-4 and lose dual channel.
2) Run in dual channel but at 2133 MHz
3) Run just 2 sticks of aftermarket at 2666 MHz
I'm leaning towards option 2. I'd rather have the extra 8GB memory at the slower speed, I'm not sure I will notice any difference in actual usage.
Probably in your case, between 24GB at 2133 and 16GB at 2666, you are right with option 2). However anyone that got 32GB or above, I think would be better with option 3). If you can I would buy another 2 of those.
Sorry to hear that. Your approach seems sensible, and it really depends on your usage. You've got both sets on hand, so you've got options moving forward. I just ended up ordering another set of the Crucial RAM for four identical sticks, and all are working as expected and playing nice together.
Ok so my geek bench scores with stock 8GB were 1202 and 5832 on my tier 2 iMac.
I installed the addition 2 crucial 16GB using the 9to5 Mac way, slots 1 and 2,16GB. Slots 3 and 4, 4GB.
Clock speeds of ram hasn’t changed and my geekbench score is now 1299 and 5800. So about the same as before.
Am I all good then, or shall I try and just use the two 16GB crucial in slots where the original Apple ram was?
Edit. Interesting tidbit the About this Mac information window wouldn’t show the clock speed of the ram like it normally does. It just showed 40GB. However within additional information screen it showed all ram as correct speed.
I installed the addition 2 crucial 16GB using the 9to5 Mac way, slots 1 and 2,16GB. Slots 3 and 4, 4GB.
Clock speeds of ram hasn’t changed and my geekbench score is now 1299 and 5800. So about the same as before.
Am I all good then, or shall I try and just use the two 16GB crucial in slots where the original Apple ram was?
Edit. Interesting tidbit the About this Mac information window wouldn’t show the clock speed of the ram like it normally does. It just showed 40GB. However within additional information screen it showed all ram as correct speed.
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Ok an update. I removed all ram and just installed the two Crucial 16GB in slots 2 and 4 where the original ram was located. Ran geekbench and results 1333 and 6899.
Thanks for the update! I would still try it with the 16GB where the Apple RAM originally was. You should be into the 6000s with you're multi-core score.
Thanks for checking that. Yeah, that sore is in line with expectations. That difference is your dropping dual channel, as you noted earlier.
Much appreciated. Just goes to show one can’t put all their faith in YouTube videos.
Sorry, haven't difficulty following all this as I'm not that technical. What was the final recommendation? I bought the extra 32GB from OWC and had plan to add it to Apple's 8GB for a total of 40GB. My needs are relatively basic.
I'm in a particularly unique situation as I have two stock Apple 16GB sticks, and want to add two aftermarket 16GB sticks for a total of 64GB of ram. since they will all be 16GB sticks, I wonder if I will have the same issues.
I wonder too. I think that the only compatibility issues we've encountered on here have been with stock 4GB sticks. Not to say that the stock 8GB sticks won't also have the same issues.
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Well, it depends. If your needs are basic, as you say, you may just want to remove the Apple RAM and install the OWC in its place. Use Activity Monitor to keep an eye on your memory pressure to see if you're using your swap. It used to be the case (back in the days of mechanical HDD) that if you started to eat into your swap significantly you knew that you needed to add more memory. But if you find that this is only happening occasionally, then you might be okay just leaving it alone since the SSD speeds are so good these days and that may suffice for your usage.
All that we know right now is that we have evidence that there is an issue mixing Apple's stock RAM with aftermarket RAM in this year's 27-inch iMacs. Perhaps it's a firmware bug, perhaps it's by design. We don't really know why we can't mix them and keep both 2667 MHz and dual channel. Apple's RAM is obviously fully compatible with the new iMacs, as are the 3rd party RAM options recommended elsewhere in these forums, it's just when mixing them that we're encountering issues.
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Good info in here. I am learning. So if we have any number in Swap used that means that the system has run out of RAM and is using the hard drive? my 2011 iMac has been doing this for years. I will be sure to order a lot more RAM for the 2020!
Exactly. Swap aka page file (more or less). Temporarily storing RAM on the HDD/SSD. Some swap usage is usually inevitable once in a while, but if it's a consistent, day-after-day thing then it may be an indication that you have insufficient memory for your use case. When it was a 7200RPM mechanical drive used for page or swap it was more of an issue, but with Apple's SSDs it is much less so, especially for more casual users.
Thank you. I will give that a try. I think 32GB should be sufficient for my needs.
Would this suggest "no dual channel at all" unless you have Ram of the same "batch" (?) of the same manufacturer?
This is what the early reports suggest. You can either have 2667 speed or dual channel, but not both when you mix Apple's OEM RAM with compatible 3rd party RAM. I don't know if "batch" necessarily matters. I initially ordered a single pair of Crucial RAM to augment the stock RAM, encountered the above issues, then ordered another batch of the same Crucial RAM. Right now everything is working as expected. The post you cite seems to suggest that batch does make a difference, but what "batch" really means for this context is still up in the air.
I don´t have the iMac here yet. But i already got 32gb CT2K16G4S266M RAM by Crucial sitting here waiting.
Are we certain T2 dos not work some magic here were "no dual channel" is not showing any drawbacks? I am not looking forward to spending another 130-140€ on 32gb extra right now because "later it could be a different batch". W00t?!
I feel your pain. Your question about the T2 is beyond my level of knowledge, but a few of us have run benchmarks confirming a performance penalty when running both Apple OEM RAM and 3rd party RAM, and which seem to be independent of the particular brand of 3rd party RAM.