Sadly I have not read these discussions before buying 2x8GB , being stunk in 24GB 2133MHz, otherwise I would buy 2x 16 instead, which as you said, is cheaper than 4x8GB.
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Memory upgrade troubleshooting in 2020 27-inch iMacs
- Thread starter KrazyKanuck
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AFAIK, you can only check dual channel indirectly. I do not know of any utility for MacOS that says explicitly "you are running in dual channel mode."
The only way I know is to run a RAM transfer speed test, such as using Novabench's RAM speed test. For this iMac the RAM transfer speed should be about 28,000+ MB/s, otherwise it is either running at a reduced clock speed (like 2133 MHz) or not running in dual channel.
In any case, what matters is that the RAM is performing at its full speed (about 28,000+ MB/s for this iMac).
Following screenshot is without GPU test, btw:
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I have 2 x 32 GB of RAM to get to 64 GB. I am running at 2667 Mhz and in dual channel according to CPU-Z in Windows.
In reality, 2133MHz vs 2667MHz is not as much of a performance hit as it sounds. It is only one minor factor in the overall performance. IMO you are still better off with 24MB at 2133 MHz than 16MB at 2667 MHz.
Oh.
Well it is true for me, for most works I will do on the machine. I don’t play games, not those games requiring high spec machine, no video editing, mostly office work and other light jobs, with sometimes virtual machine and light photo editing using software provided by camera manufacturer, like DDP by Canon.
For me, 2133MHz vs 2667MHz most probably do not have a big difference practically, 2667MHz is more on the mental or feeling side; and 24GB is more practical for me, more ram is better for running virtual machine and multiple tasks that don’t require fast ram like video games or video editing usually do.
Hi all
I´ve just run a RAM test with CPU-Z on windows 10 (bootcamp) on my iMac 27" 2020, i7 8 Cores with 5700XT.
Seems like if you conect in the right order you can get 2666mhz and dual channel even if the memories aren´t 100% identical between them.
Here some pictures.
Can I now say I´m safe running 4gb-4gb-32gb-32gb in 2667Mhz DUAL?
Thank you
I´ve just run a RAM test with CPU-Z on windows 10 (bootcamp) on my iMac 27" 2020, i7 8 Cores with 5700XT.
Seems like if you conect in the right order you can get 2666mhz and dual channel even if the memories aren´t 100% identical between them.
Here some pictures.
Can I now say I´m safe running 4gb-4gb-32gb-32gb in 2667Mhz DUAL?
Thank you
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Well, it just show that iMac DOES support Flex memory mode.
However, in your case, you get 16GB of RAM in dual channel only, while the rest 56GB is in single channel.
CPU-Z cannot differentiate flex mode from real full dual channel.
I suggest run Novabench RAM speed test and run Geekbench 5 multicore test for:
a) 4-4-32-32
b) empty-32-empty-32
and report back.
(Do it several times and report the maximum)
I suspect you will be disappointed in the results from a). I was.
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Just asking cos I don't know if Geekbench 5 or nova bench works on Mac.
I ran Novabench on my iMac for the heck of it. Ran 3 tests to see if there were any wide variances between test runs, but there were not. 5700XT GPU reported a score of 558 on all tests. RAM speed had the widest variance, with values between 28,860 and 29,743MBytes/second. This is 2 32GB sticks of Crucial RAM. CPU score was between 1627 - 1634 for the i7-10700K.
Yes, RAM speed of about 29,000 MB/s is what you want to see.
If the RAM is not performing optimally, it will drop to about 25,000 MB/s. Not a huge drop, but still.
btw, the Novabench GPU test is not a good test as it tops out at 60 fps, so almost always gives a score of 558.
I wonder if the GPU test is locked to the refresh rate of the display? I don't have a 144Hz display to test this theory with though.
Thanks for the info, I was surprised to see only 60FPS in the GPU test.
I think the software isn't sensitive enough or yeah it might be sync with display refresh rate.
Finally had the chance to run the Novabench and Geekbench5 for the ram.
NOVAVENCH:
4gb-4gb-32gb-32gb = 18432mhz
None-32gb-None-32gb = 29614mhz
Definitely I'm removing my 4gbx2.
CPU: from 1592-1629
Geekbench 5:
CPU single core- 1285
CPU multi core- 6957
NOVAVENCH:
4gb-4gb-32gb-32gb = 18432mhz
None-32gb-None-32gb = 29614mhz
Definitely I'm removing my 4gbx2.
CPU: from 1592-1629
Geekbench 5:
CPU single core- 1285
CPU multi core- 6957
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I figured just game the system and put in the full 128GB of RAM from OWC. The iMac burped and went on its merry way. There's something occasionally very satisfying about massive overkill.
Okay guys, I’m hopefully going to order an 8-core i7 iMac on Friday. I want to order 32 gigs of RAM for it. Will installing the new RAM along with the stock RAM give me any headaches or run slowly (it would be nice to run the full 40 gigs of ram total) or should I just roll with the 32 and toss Apple’s 8 gigs into a drawer? Also, who’s RAM is better, OWC’s or Crucial’s. Any and all help would be appreciated, thanks.
Thanks for doing this and confirming mixing RAM sizes is not optimal.
Your Geekbench 5 multicore should be about 8900 for the i7, or near 10,000 for the i9, if everything is working correctly and you don't have some background process hogging the CPU. 1698 does not look right
Put in 32GB (I suggest 2x16GB sticks) and toss Apple's 8GB.
There are different opinions on RAM brand: I suggest Crucial if available, otherwise OWC or Timetec are both fine (IMO). Just make sure they say they are "made for Mac," as they then have lifetime guarantee to be compatible. Crucial make sticks some of which are for Mac some not. I don't know if there is really any difference between them, but better to get the ones they recommend for Mac.
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