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Is this dual channel or not? And how can I tell.

Luca Allard

Luca Allard

macrumors newbie
Original poster
Sep 5, 2020
4
1
I got the new 2020 iMac 27" with factory installed 16GBs of ram. I bought 2 8GB sticks of OWC ram. Both the Apple factory ram and the OWC ram were 2667MHz. At first I installed them in the 1 & 3 slots (Apple) and 2 & 4 slots (OWC). The RAM then showed 32GB at 2133MHz. Then I but the Apple RAM in slots 1 & 2 and the OWC RAM in slots 3 & 4. The system check then said I have 32GB of RAM at 2667MHz.

I then read some post that said if I configure it like I did at the end, I would be running a single channel as opposed to a dual channel. Is this true? How would I know? I can I check to see?

Any advise or comments would be greatly appreciated.
 
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Yes, this is true - Bank 1 and 3 is one channel, bank 2 and 4 is another channel. - Doing a memory benchmark might give you some more concrete details about the speed differential it might have.
 
casperes1996 said:
Yes, this is true - Bank 1 and 3 is one channel, bank 2 and 4 is another channel. - Doing a memory benchmark might give you some more concrete details about the speed differential it might have.
Click to expand...

No that's not right.

OP, Channel 1 and 2 are the same Channel and Channel 3 and 4 are the same channel. If you have 8GB in each of the slots you should be getting dual channel. But I'd keep slots 1 and 3 either both Apple and 2 and 4 both OWC and wouldn't mix and match them.

If you look at System > Memory and look at the slots you'll see all 4 slots with the Channel in parenthesis. Channel A for slots 1 and 2 and Channel B for Slots 3 and 4. If you were only using 2 sticks of memory you would either want to fill 1 and 3 or 2 and 4 to get dual channel. As long as all four slots are reading 2667 MHz then you are getting dual channel because each channel is filled with memory.
 
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Donnation said:
No that's not right.

OP, Channel 1 and 2 are the same Channel and Channel 3 and 4 are the same channel. If you have 8GB in each of the slots you should be getting dual channel. But I'd keep slots 1 and 3 either both Apple and 2 and 4 both OWC and wouldn't mix and match them.

If you look at System > Memory and look at the slots you'll see all 4 slots with the Channel in parenthesis. Channel A for slots 1 and 2 and Channel B for Slots 3 and 4. If you were only using 2 sticks of memory you would either want to fill 1 and 3 or 2 and 4 to get dual channel. As long as all four slots are reading 2667 MHz then you are getting dual channel because each channel is filled with memory.
Click to expand...

... You say that what I wrote is not right, and then go on to repeat what I said?
 
Donnation said:
You said bank 1 and 3 is one channel and 2 and 4 are one channel, and that’s not right. Bank 1 and 3 are two channels and 2 and 4 are two channels.
Click to expand...

The regular iMac is not quad channel. You said it right in your post before. Oh wait... Hold on... No wait, you’re right, I mixed it up, sorry. Very sorry, I meant to say that bank 1 and 2 and 3 an 4 are each a channel, so 1 and 3 & 2/4 would each make up a dual channel setup.
You’re totally right, my bad, apologies again 😅. Brain fart on my behalf
 
Is the OP saying that by actually mixing up the manufacturer across the two pairs of banks (same size all chips) then it’s actually working in the higher speed AND dual channel? So it that a fix to the people reporting problems with using stock ram and adding in two more? Good but counterintuitive if so...
 
casperes1996 said:
The regular iMac is not quad channel. You said it right in your post before. Oh wait... Hold on... No wait, you’re right, I mixed it up, sorry. Very sorry, I meant to say that bank 1 and 2 and 3 an 4 are each a channel, so 1 and 3 & 2/4 would each make up a dual channel setup.
You’re totally right, my bad, apologies again 😅. Brain fart on my behalf
Click to expand...

Haha, no problem. Cheers!
 
Luca Allard said:
I got the new 2020 iMac 27" with factory installed 16GBs of ram. I bought 2 8GB sticks of OWC ram. Both the Apple factory ram and the OWC ram were 2667MHz. At first I installed them in the 1 & 3 slots (Apple) and 2 & 4 slots (OWC). The RAM then showed 32GB at 2133MHz. Then I but the Apple RAM in slots 1 & 2 and the OWC RAM in slots 3 & 4. The system check then said I have 32GB of RAM at 2667MHz.

I then read some post that said if I configure it like I did at the end, I would be running a single channel as opposed to a dual channel. Is this true? How would I know? I can I check to see?

Any advise or comments would be greatly appreciated.
Click to expand...
run geek bench to check. @Azrael9 has the same setup as i do i9, 5700 XT and his geekbench was 5k while mine was near 10k. it becuase he was mixing apple ram with third party in the 2020 imacs and losing duel Channel but keeping the 2667 speed

basily you dont mix third party with apple ram. cuzz u will either lose the 2667 speed and lose duel channel or keep deul channel at 2133
 
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Wait, so if I have APPLE RAM (2 X 8GB) 2667MHz RAM in Slot 1 and Slot 2 AND OWC RAM (2 X 8 GB) 2667MHz RAM in Slot 3 and Slot 4.....I am then running 2667MHz at 32 GBs BUT in SINGLE CHANNEL and not DUAL CHANNEl??

If I put an APPLE RAM in slot 2 & 4 AND I put OWC RAM in slot 1 & 3 then I have 2133NHz AND DUEL CHANNEL??

Can someone explain this so I can understand? I have a lot of friends who do not understand as well. I really appreciate the collective intelligence on this one. I just don't get it. Many thanks for your patience and understanding.
 
Luca Allard said:
Wait, so if I have APPLE RAM (2 X 8GB) 2667MHz RAM in Slot 1 and Slot 2 AND OWC RAM (2 X 8 GB) 2667MHz RAM in Slot 3 and Slot 4.....I am then running 2667MHz at 32 GBs BUT in SINGLE CHANNEL and not DUAL CHANNEl??
Click to expand...
Exactly.
Luca Allard said:
If I put an APPLE RAM in slot 2 & 4 AND I put OWC RAM in slot 1 & 3 then I have 2133NHz AND DUEL CHANNEL??
Click to expand...
exactly.
But not recommended at all.

I don’t see what’s more to explain.


Rules of thumb :
  1. Do not mix RAM modules with different capacity/speed/manufacturer. A OWC memory kit with Hynix ICs won't work with an OWC memory kit with Micron ICs, even if they are "For Mac", with the same speed, timings, comes from the same manufacturer, and other specs.
  2. If you chose to upgrade to, for example, 2x32 GB, and have 2 memory slots for future upgrade, chose Crucial RAM. It's the only RAM brand which has a unique ICs manufacturer which is Micron. Kingston usually have a locked BOM for ValueRAM Server RAM, but I can't find the same information for Mac RAM.
  3. No experiment 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.
  4. Memory must be installed in slot 1-3 and 2-4 when in kit of 2 SODIMM modules. If all 4 SODIMM are populated, make sure all ICs are coming from the same manufacturer. If not, dual channel is lost.
See https://forums.macrumors.com/threads/memory-upgrade-compatibility-list-for-imac-2019-2020.2248911/
 
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If you’re looking for 32GB RAM sticks, I'm exceedingly happy with Samsung. Model number is M471A4G43MB1 and it’s like $120 a stick from Amazon. Like Micron (Crucial), Samsung is also its own IC manufacturer. The RAM isn’t certified for Mac but it has the same timings and same specs as any of the other stuff.
 
Whiteman007 said:
run geek bench to check. @Azrael9 has the same setup as i do i9, 5700 XT and his geekbench was 5k while mine was near 10k. it becuase he was mixing apple ram with third party in the 2020 imacs and losing duel Channel but keeping the 2667 speed

basily you dont mix third party with apple ram. cuzz u will either lose the 2667 speed and lose duel channel or keep deul channel at 2133
Click to expand...

True.

Azrael.
 
There must be a way to get the iMac to report whether its running dual channel or not directly surely? Rather than rely on inferences from benchmark results.
 
According to Apple's own documentation on RAM installation updated on 9-2-2020,

Channel A is slots 1&2 and Channel B is slots 3&4.

They recommend mixed RAM (i.e. RAM that is not identical in every way), be installed in slots 1&2 and then 3&4.

If you have 4 identical sticks it doesn't matter which 4 slots you use. If two are from one manufacturer and 2 from another, you can't get dual channel support, but they must be installed in with the two from one manufacturer in slot 1&2 and the two from the other manufacturer in slot 3&4 if you want the correct speed reported.
 
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Totally confused!

I removed both OEM sticks and replaced with 2x 16GB from Crucial.....

Am I in Dual Channel Mode????

Any replies would be appreciated!


iMac memory.png



EDITED to add - 2020 iMac - i7, 5700XT, 1TB
 
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casperes1996 said:
Yeah that'd be dual-channel 2667Mhz - If you ever want to go to 64GB I recommend getting as identical sticks as you can for the two remaining slots :)
Click to expand...

Thanks for replying.

I almost went for 64GB just to simplify the Dual Channel question...........but it would be overkill for my needs.

First iMac and I'm loving it !
 
Kb4791 said:
Thanks for replying.

I almost went for 64GB just to simplify the Dual Channel question...........but it would be overkill for my needs.

First iMac and I'm loving it !
Click to expand...

Yeah; I consider myself a really heavy user and 64 would be overkill for me too at this time, so I got 32 as well :)

The whole dual channel thing isn't really a discussion at all if you're getting identical RAM and you install them in paired slots like 1&3 or 2&4 :)
 
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I still don't understand how to confirm if it runs in dual channel mode, can someone explain plainly, what indicators to look for exactly?
 

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yoli said:
I still don't understand how to confirm if it runs in dual channel mode, can someone explain plainly, what indicators to look for exactly?
Click to expand...
There is no indicator that will tell you "you are running in dual channel mode." (at least not easily on a Mac).

There are two separate things of relevance: dual channel, and transfer speed (MHz).
Dual channel:
Dual channel means that the memory controller can simultaneously access memory in Channel A (aka Bank 0) and in Channel B (aka Bank 1) in parallel, thus effectively doubling the memory transfer speed. For this to happen, the size of sticks in Channel A should be the same as the size of sticks in Channel B. The requirement for full dual channel is Channel A GBs matches Channel B GBs. "Channel" is also known as "Bank." You can see from your screen shot that Bank 0 (i.e., Channel A) has 8GB, and Bank 1 (i.e., Channel B) has 8GB. Therefore, by deduction, you are running in dual channel.

The other relevant information is that each memory stick is running at full speed (in your case, 1600 MHz). This is separate from dual channel.

Hope this helps
 
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Sorry to dig up an old thread but I have a very similar question.

I wanted to add 2 x 4 GB to my imac 2020 to make the total go to 16 GB. I found 2 SK Hynix modules which are exact same spec and differ only by 1 letter in the serial number. I though this would be OK to add to slot 1 and 3, But the memory now runs in 2133mhz.

I read I can change the apple ram to slot 1 and 2 and the new ram to slot 3 and 4 but will then lose dual channel support. But is this also the case with 4 x 4 GB modules? If not, will 4x 4 GB of the exact same serial number work without problems? i may be able to find the exact same serial number hynix modules.

I hope anyone can have the definitive answer. Thank you!
 
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