Mixed RAM in 2020 iMac. Does it disable dual channel mode?

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Mixed RAM in 2020 iMac. Does it disable dual channel mode?

I've installed new 2x16 GB RAM chips in slots 1 & 2 on my 2020 iMac, leaving the original Apple 2x4 GB chips in slots 3 & 4. Everything works fine at 2667 MHz. However, the chip vendor states that dual channel mode is disabled unless you either upgrade all 4 slots with new matching chips or install a new matched pair into slots 1 & 3 and leave slots 2 & 4 empty. I don't know what "dual channel mode" actually is or why it's important, but is it true that installing new RAM chips alongside the Apple ones will hinder the performance of the machine? Thanks for any advice or explanation!

iMac 27″, macOS 11.2

Posted on Mar 22, 2021 10:51 AM

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Answer 1

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rkaufmann87

Level 10

140,982 points

Mar 22, 2021 6:40 PM in response to HWTech

Please note my 2020's RAM's installation. It's a 2020 27" that I upgraded to 40GB using the original 8GB of RAM and OWC (www.macsales.com) RAM. Please pay careful attention to the slots used and the RAM's speed. I'v been using this setup since August 2020 with ZERO problems. From your description it appears you got it right so just leave it alone.

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Answer 2

Howto101 Author

Level 1

8 points

Mar 23, 2021 2:09 AM in response to rkaufmann87

Thanks for helpful answers. My original issue got complicated by the fact that the OWC chips were most likely faulty. I've installed 2x16 GB chips from Crucial into slots 1 & 2 with the Apple ones in slots 3 & 4 and all works fine now. Placing them in the slots left free by Apple made all 4 chips run slow (2100 Mhz). I'll attach the vendor's thing about dual channel mode if you're interested. Yes I did wonder if it was just a way to get people to buy 4 instead of 2. I'll stay with what I have.

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Answer 3

den.thed

Level 9

77,656 points

Mar 22, 2021 1:53 PM in response to Howto101

Which vendor?

Some would love to sell you 4 modules instead of only 2 modules.

From everything I seen and read around here, you have installed the modules in the correct orientation. If you didn’t, then the module speed would show a lower speed.

As for dual chaneling, more RAM of the same speed always trumps less RAM.

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Answer 4

HWTech

Level 9

56,168 points

Mar 22, 2021 5:53 PM in response to Howto101

Dual Channel Mode is more difficult today than it was years ago. I know in the generic PC world that most times it is recommended to have each stick of RAM be from the same manufacturer, the same specs, and made on the same production run to ensure the memory will work properly with each other. I haven't had to worry about optimal memory performance in years as I haven't custom built a PC in years.

As @den.thed mentions having more memory is more important than worrying about dual channel mode. The extra performance from dual channel mode won't be noticeable with most work loads.

You may want to put the newer larger memory sticks in the slots occupied by the original Apple memory and install the original Apple memory in the slot that were open from the factory.

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Mixed RAM in 2020 iMac. Does it disable dual channel mode?

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