Suggestions on how to mix RAM sticks on 2019 iMac? (numbered diagram)

[Turnpike]

So I have a 2019 27" iMac, and have new additional RAM memory arriving in a couple of hours.

Right now I have 4GB and 4GB and have 32GB and 32GB memory arriving shortly.

Is there a way I should install the 2 32GB sticks, and would it help or hurt to throw the 4GB sticks in the empty slots?

Here's a picture from Google Images, my plan is to put the new (OWC 32GBx2) sticks in the #2 and #4 slots, and the 4GB's in the two empty slots, does that look right, or is there a configuration that would work better like if they are side by side?

Thanks in advance, there's nothing like knowing you're making the most of the RAM when it's your daily machine you spend half your life on.

 

[Andrey84]

So I have a 2019 27" iMac, and have new additional RAM memory arriving in a couple of hours.

Right now I have 4GB and 4GB and have 32GB and 32GB memory arriving shortly.

Is there a way I should install the 2 32GB sticks, and would it help or hurt to throw the 4GB sticks in the empty slots?

Here's a picture from Google Images, my plan is to put the new (OWC 32GBx2) sticks in the #2 and #4 slots, and the 4GB's in the two empty slots, does that look right, or is there a configuration that would work better like if they are side by side?

Thanks in advance, there's nothing like knowing you're making the most of the RAM when it's your daily machine you spend half your life on.




View attachment 2456988

Here is the official guide:

Install memory in an iMac – Apple Support (UK)

Get memory specifications and find out how to install memory in iMac computers.

support.apple.com

"If your DIMMs are mixed in capacity, minimise the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4) when possible."

So, technically, your approach to install one stick of the new memory into Channel A (slot #2) and the second one into Channel B (slot #4) is correct. However, I read on here how mixing the RAM incorrectly can not only disable dual-channel (which you are addressing), but it can also reduce the memory frequency, which can noticeably reduce performance.

"For optimal memory performance, DIMMs should have the same capacity and speed, and be from the same vendor."

Based on this principle from Apple, my personal recommendation is to install your new 2 x 32 GB modules where your 2 x 4 GB are now. Then, get rid of the old memory.

Did you mention your current RAM is installed into slots 2 & 4? It's best to use the slots which were already selected by Apple.

 

[gilby101]

Here's a picture from Google Images, my plan is to put the new (OWC 32GBx2) sticks in the #2 and #4 slots, and the 4GB's in the two empty slots, does that look right, or is there a configuration that would work better like if they are side by side?

That should work well.

Simple rule:
Slots 1 and 3 the same.
Slots 2 and 4 the same.

So in your case slots 1 to 4 as either 4,32,4,32 or 32,4,32,4.

So long as they are paired like that, the 2019 iMac is fairly robust for mixing RAM size and vendor. Many of the contrary stories you may have heard might be for 2020 iMacs for which there can be problems unless all 4 are identical (size and vendor). Also see my last paragraph below in response to Audrey84.

Initially I ran my 2019 iMac with original 4+4GB (from Apple) with 16+16GB (OWC). I now have 16+16 and 32+32 (all from OWC).

Ps. The first boot after a change of RAM can take about a minute before you see anything. Rather alarming if you don't expect the delay.

However, I read on here how mixing the RAM incorrectly can not only disable dual-channel (which you are addressing), but it can also reduce the memory frequency, which can noticeably reduce performance.

Probably that was for 2020 iMac, not the 2019 iMac.

I don't know wether you noticed but the Apple Support page you linked says "For optimal memory performance, DIMMs should have the same capacity and speed, and be from the same vendor" for the 2020 iMac, but leaves that out for the 2019 and older.

 

[pshufd]

Based on this principle from Apple, my personal recommendation is to install your new 2 x 32 GB modules where your 2 x 4 GB are now. Then, get rid of the old memory.

That was my thought too. The 8 GB is marginal and it would be easier to just leave it out unless you absolutely needed it and then I'd think about ordering another two sticks.

 

[Andrey84]

That should work well.

Simple rule:
Slots 1 and 3 the same.
Slots 2 and 4 the same.

So in your case slots 1 to 4 as either 4,32,4,32 or 32,4,32,4.

So long as they are paired like that, the 2019 iMac is fairly robust for mixing RAM size and vendor. Many of the contrary stories you may have heard might be for 2020 iMacs for which there can be problems unless all 4 are identical (size and vendor). Also see my last paragraph below in response to Audrey84.

Initially I ran my 2019 iMac with original 4+4GB (from Apple) with 16+16GB (OWC). I now have 16+16 and 32+32 (all from OWC).

Ps. The first boot after a change of RAM can take about a minute before you see anything. Rather alarming if you don't expect the delay.


Probably that was for 2020 iMac, not the 2019 iMac.

I don't know wether you noticed but the Apple Support page you linked says "For optimal memory performance, DIMMs should have the same capacity and speed, and be from the same vendor" for the 2020 iMac, but leaves that out for the 2019 and older.

Makes sense, but I don't trust that these issues happened only with the 2020 iMac, even though on the Apple website the warning is only for the 2020.
Also, your OWC RAM could've been the same speed as Apple, which might not be the case for the OP.
Have you run any benchmarks, like Geekbench, before and after installing the 3rd party RAM? The performance change might've been 5%, which you might have not noticed.

 

[gilby101]

Have you run any benchmarks, like Geekbench, before and after installing the 3rd party RAM? The performance change might've been 5%, which you might have not noticed.

No, I never did such tests. As you say 5% would not have been noticeable. System Information reports unchanged speed (2667 MHz).

but I don't trust that these issues happened only with the 2020 iMac, even though on the Apple website the warning is only for the 2020

Also there were the very long threads here describing the woes with 2020 iMac. None of that for earlier iMacs. I suspect that Apple felt forced to add that caveat for 2020 iMac after the problems with mixed RAM became apparent.

 

[Nermal]

Yep, the 2020 specifically is very fiddly. When I did an upgrade, I ended up having to remove the factory RAM to prevent slowdowns, whereas I'd intended to keep it.