Apple updated their RAM installation guide on 9-2-2020. It's super finicky about RAM and there is only one way to get dual channel support which requires literally identical RAM in every way.
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Memory upgrade troubleshooting in 2020 27-inch iMacs
- Thread starter KrazyKanuck
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Hard to say. I’d be willing to say no because if the pickiness of the iMac memory system.
can you measure RAM speed ? It would be a clue.
This is what I did. Honestly don’t think I’ll outgrow 64GB RAM on this machine during its lifetime.
Thanks for the sanity check. I was planning to return the Newegg pair if for no other reason than I wasn't sent what I ordered but now I'm not that confident that ordering another "identical" CT2K16G4S266M kit wouldn't have the same weirdness. So I'm opting to just return both pairs and order a single 2x32 kit as others have mentioned.
In absolutely nothing.
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It should be identical. Crucial uses only Micron chips.
All I really want is 16GB, but I don't want to pay Apple's exhorbitant price for memory. So, if I buy the base 8GB iMac do I need to buy 16GB of identical third-party memory or is it possible to just buy 8GB and run 8GB of Apple and 8GB of a carefully-chosen third-party memory and get the full speed and two-channel operation? There seems to be a stampede on this thread to assume that the 8GB of Apple memory is a throw-away, the cost of doing business the "Apple Way", and any memory upgrade has to be either all Apple or all third-party. Is that really the case??
Just put the Apple ram in slots 1 and 2 and the third party ram in 3 and 4. Get full speed and dual channel.
The way I understand it, the two don't necessarily correlate.
Dual-channel, or more accurately, memory interleaving, pertains to the memory addresses, with the controller treating different banks as a unified, contiguous bucket, not unlike the virtual volume of a Fusion drive. It is a characteristic independent of speed, and not a new trick.
In the OP's first example, splitting the matched Pairs 1 (FE) and Pair 2 (FJ) between channels A and B may have enabled interleaving, albeit at reduced speed.
In the second example, keeping Pair 1 in Channel A, and Pair 2 in Channel B allows them to both run at full speed, but doesn't necessarily indicate that interleaving is in effect, since the controller is seeing non-matched DIMMs between the channels, and not group them.
The real mystery with the '20 iMac is why the controller is dialing back the speed in conditions where the more tolerant '19 did not.
If it did not do that, the whole issue probably would have largely gone unnoticed, as no flags would have been raised, and most people would assume things were operating at optimum performance, except for those apt to run benchmarks to gauge effects from different configurations.
No — unless the 4 sticks match to the satisfaction of the T2 chip.
Yes.
The 2019 does not have a T2 controller.
So far all that I have seen post who have installed 4 of the same size and spec RAM sticks by putting the matched pairs in slots 1 and 2 and the other matched pair in 3 and 4 have kept full speed and dual channel.
So if the person above puts the 2x 4 GB sticks of Apple RAM in slots 1 and 2 and the 2x 4 GB sticks of third party RAM should maintain 2667 MHz and dual channel.
I am all ears if you want to find a person who did the config I mention and see it drop in speed or lose dual channel.
I have been reading them. Go back to post #128, #139, and #150 on page 6. Heck look at post #300 on page 12. Putting them in the config I stated results in full performance. So far the ones who have put 4 sticks of the same size and are seeing a performance drop have the matched pairs in slots 2 and 4 and the other matched pair in 1 and 3.
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Hey there! I'm planning on doing the exact same thing! Did everything pan out smoothly for you?
I'm currently looking at the 2x32 GB set (CT2K32G4S266M) from Crucial. I'll most likely just toss those in & remove the 2x4 GB stock set until I save enough for another 64GB kit.
In regards to PC speed - since Crucial's RAM is (PC4-21300) and if Apple recommends (PC4-21333) on the Install memory in an iMac page (updated on Sept. 2)... is there anything to keep in mind if I were to go ahead with using only Crucial's set?
Thanks a bunch for any wisdom you might be able to toss my way!
Cheers!
See Memory upgrade compatibility list for iMac 2019-2020 thread.Hey there! I'm planning on doing the exact same thing! Did everything pan out smoothly for you?
I'm currently looking at the 2x32 GB set (CT2K32G4S266M) from Crucial. I'll most likely just toss those in & remove the 2x4 GB stock set until I save enough for another 64GB kit.
In regards to PC speed - since Crucial's RAM is (PC4-21300) and if Apple recommends (PC4-21333) on the Install memory in an iMac page (updated on Sept. 2)... is there anything to keep in mind if I were to go ahead with using only Crucial's set?
Thanks a bunch for any wisdom you might be able to toss my way!
From top post in that thread: No experiment(s) show that mixing Apple stock RAM with aftermarket RAM listed above is correctly operating at full speed and in dual channel. Don't mix Apple RAM with aftermarket RAM.
Is this unambiguously true, that there is no configuration of Apple + aftermarket RAM that works at full speed and dual channel? I thought ways to do this had been reported in this thread.
In short, no, it doesn't work.
Long answer: It might work if you have all same capacity modules but in 1-2 and 3-4 ordering, but nothing is cristal clear on whether or not dual channel is preserved. The rule of thumb is to not mix stock with aftermarket RAM and do not mix module capacity. Buy all the RAM you need from a single manufacturer and ensure all modules have the same chip manufacturer (Hynix, Samsung or Micron). This rule is valid for any PC in this world, not only Mac.
If I order the 32gb kit from OWC ( 4 x 8gb), is OWC aware of the situation with the 2020 iMacs Being so picky with the ram installation and requiring modules to be identical? Do they actually Check and ensure the 4 modules In the kit are identical before shipping them out to the customer or is it a crap shoot of not knowing what they’ll actually ship to me?
Yes, since it's a kit of 4 the modules will have all the same ICs for sure. It doesn't let you upgrade in the future thought.
That’s great to know, 32GB is honestly plenty of Ram, I could go for 64 kit but it’s double the price
Well what do you do? 64 is obviously better but I’m not sure I want to spend over $250 for 64 gigs and 32 is sure better than 8gb lolFor me 32 GB is 1/2 of my daily memory usage