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Problems with installing new memory in the new 2020 27" iMac

camner

macrumors regular
Original poster
Jun 19, 2009
195
6
I ordered 2x32GB kit from OWC to replace the stock 8GB RAM. I couldn't get the iMac to boot with the OWC RAM. I put the original Apple sticks back in, and the computer wouldn't boot then, either. After a number of attempts (about 6), I finally got the iMac to boot with the stock memory. It appears that my new iMac is very sensitive to exactly how the DIMM sticks are positioned (at least that's the only thing I can think of to explain it).

I then tried adding the OWC memory to slots 1 & 3 withOUT removing the Apple RAM, and lo and behold, the iMac booted! But try as I might, I couldn't get the iMac to boot with OWC memory only in the machine.

So, I then put back in all 4 sticks (2xApple + 2xOWC), but it took a couple of tries to get the iMac to boot. I then removed the stock RAM from slots 2 & 4, leaving the OWC RAM in slots 1 & 3, and the iMac boots just fine. System Report says I've got 64GB running at 2666MHz.

So, two questions:
  1. Is the VERY finicky nature of the RAM insertion/replacement process something I should think of as a defect worthy of taking up with Apple?
  2. Is there any reason I shouldn't be happy with two OWC sticks in slots 1 & 3 instead of 2&4? I'm getting 2666MHz, I know. Am I getting dual channel with this config?
 
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Donnation

Suspended
Nov 2, 2014
1,686
2,065
Its funny to see this, as I had the exact same issue when I originally installed RAM in my 2020 iMac. I have memory in slots 1 and 3 as well, and initially the iMac would not boot. I could not figure out what the heck was going on. I even got Apple support involved. They didn't really know what the issue was, but after pulling the memory out and placing it in again it booted without issue.

Since then, its worked and booted on fine so I don't know what the heck the non booting is all about initially.

And to answer your question, yes you are getting dual channel in slots 1 and 3. As far as taking it up with Apple, they won't have any clue what you are talking about but will offer to send you a new one if you want (that's what they offered me). I told them no for now but if they issue came up again that I would be asking for a new unit to be sent out to me and they said that would be fine. As I said though, no issues since that initial problem.
 
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camner

macrumors regular
Original poster
Jun 19, 2009
195
6
Thanks for your reassuring reply (well, reassuring about the slots, not so much about the iMac's finicky RAM replacement!)
 
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Silencio

macrumors 68020
Jul 18, 2002
2,484
340
NYC
I'm curious about others' experiences with this. I have a couple of 2020 27" iMacs on the way, but I ordered 4x16GB SODIMMs to upgrade them to 64GB. We'll see if that makes a difference, though my systems aren't due to ship for another 7-10 days.
 
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Ruz

macrumors newbie
Sep 1, 2020
7
0
I'm curious about others' experiences with this. I have a couple of 2020 27" iMacs on the way, but I ordered 4x16GB SODIMMs to upgrade them to 64GB. We'll see if that makes a difference, though my systems aren't due to ship for another 7-10 days.
I got 32GB from OWC (2x16GB). When the iMac came, I pulled out the Apple RAM and installed the OWC RAM in the same slots. Never had an issue with booting the machine.
 
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camner

macrumors regular
Original poster
Jun 19, 2009
195
6
I got 32GB from OWC (2x16GB). When the iMac came, I pulled out the Apple RAM and installed the OWC RAM in the same slots. Never had an issue with booting the machine.
I have changed the RAM in countless Macs over decades (usually with RAM from OWC), including a previous 27” iMac (2015). I have NEVER had this kind of problem before. I know how to do this. Occasionally I had to reseat the RAM a second time. Nothing like this.

I hope this isn’t a sign of a machine that is “on the edge.” I did get AppleCare, so I have 3 years during which I can take it to Apple, but I intend to keep this machine longer, perhaps much longer.
 
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Zltnnd

macrumors newbie
Aug 28, 2020
7
1
I ordered 2x32GB kit from OWC to replace the stock 8GB RAM. I couldn't get the iMac to boot with the OWC RAM. I put the original Apple sticks back in, and the computer wouldn't boot then, either. After a number of attempts (about 6), I finally got the iMac to boot with the stock memory. It appears that my new iMac is very sensitive to exactly how the DIMM sticks are positioned (at least that's the only thing I can think of to explain it).

I then tried adding the OWC memory to slots 1 & 3 withOUT removing the Apple RAM, and lo and behold, the iMac booted! But try as I might, I couldn't get the iMac to boot with OWC memory only in the machine.

So, I then put back in all 4 sticks (2xApple + 2xOWC), but it took a couple of tries to get the iMac to boot. I then removed the stock RAM from slots 2 & 4, leaving the OWC RAM in slots 1 & 3, and the iMac boots just fine. System Report says I've got 64GB running at 2666MHz.

So, two questions:
  1. Is the VERY finicky nature of the RAM insertion/replacement process something I should think of as a defect worthy of taking up with Apple?
  2. Is there any reason I shouldn't be happy with two OWC sticks in slots 1 & 3 instead of 2&4? I'm getting 2666MHz, I know. Am I getting dual channel with this config?
I had a similar problem with mine. Try pushing the memory modules inward as you rotate the whole assembly back into its locked position. Without the inward pressure the memory sticks tend to move back out when the assembly is rotated into locked position. And yes there is a stupid problem with these assemblies.
 
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pmiles

macrumors regular
Dec 12, 2013
177
63
Apple updated their RAM installation documentation on 9-2-2020 to address the issues customers are seeing with this Mac and RAM installation. In a nutshell, all sticks of RAM need to be identical in spec, capacity, and vendor in order to achieve dual channel support. If it interprets 2 sticks as being from manufacturer X and two from manufacturer Y even if the packaging that came with the RAM said they were all the same, it's not going to have dual channel support... it's considered mixed RAM.

Mixed RAM, capacity or manufacturer needs to be installed in slots 1&2 then 3&4.

Apple calls slots 1&2 Channel A and slots 3&4 Channel B.

The assumption is everyone is installing RAM in pairs of identicalness... so nothing has been said about only using 3 slots in the new machine or say 4 sticks of identical spec but different manufacturers. I suspect those scenarios would result in lower speeds being reported than they should be.
 
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camner

macrumors regular
Original poster
Jun 19, 2009
195
6
I had a similar problem with mine. Try pushing the memory modules inward as you rotate the whole assembly back into its locked position. Without the inward pressure the memory sticks tend to move back out when the assembly is rotated into locked position. And yes there is a stupid problem with these assemblies.
Thanks for the tip. That wasn't necessary with my 2015 27" iMac; I just had to swing the arms back to the locked position. I'll try your suggestion.
 
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EvilCo_E

macrumors newbie
Sep 7, 2020
4
1
I ordered the wrong ram at first (2x16gb) and it only ran at 2133Mhz (with and without the 8gb Apple ram), then I got 4x16gb of proper crucial ram and now it works perfectly at 2667Mhz. I've replaced the ram and fiddled around with it quite a few times but I've never had the machine not boot. One of the slots never really made a clicking sound like the rest did but it worked fine.

I've had a completely different sort of ram related ordeal, the ram door wouldn't fit in properly (one of the sides was sticking out) so I took it out and put it back and it stayed the same. So then when I pressed the button to release the door again 3 of the little hinges broke clean off the ram door. So now I'm stuck with a piece of paper on the hole to prevent dust from going in until my replacement door arrives. I think that's apples revenge for me not buying their ram Lol.

So yeah an unlucky day for me that was, although I just found it quite hilarious in the variety of problems I had with the ram replacement experience.
 

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lukasz74nj

macrumors member
Oct 19, 2012
32
0
I ordered 2x32GB kit from OWC to replace the stock 8GB RAM. I couldn't get the iMac to boot with the OWC RAM.
In my case it took a very long time to boot (black screen, no sound) after replacing the memory but it is all good since then. It was more challenging to open the RAM door - Lego Technic, Liftarm (32017) does the job pretty well.
 

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camner

macrumors regular
Original poster
Jun 19, 2009
195
6
In my case it took a very long time to boot (black screen, no sound) after replacing the memory but it is all good since then. It was more challenging to open the RAM door - Lego Technic, Liftarm (32017) does the job pretty well.
How long was "a very long time." When I finally got it to boot, it was about 45 seconds the first time it booted.
 
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hellfried

macrumors regular
May 3, 2008
107
10
Penang, Malaysia
In my case I removed the Apple ram, replaced them with 8G x 2 of Crucial memory. It booted up after a small delay of about 5 seconds. One week later another 2 sticks of 8G Crucial memory arrived from a different vendor. After installing them the computer again took an extra 5 seconds to boot up and its all good. Now I have 32G of memory running at 2667 MHz.
 
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UFallingRock

macrumors newbie
Sep 13, 2019
24
23
I had a similar problem with mine. Try pushing the memory modules inward as you rotate the whole assembly back into its locked position. Without the inward pressure the memory sticks tend to move back out when the assembly is rotated into locked position. And yes there is a stupid problem with these assemblies.

Thank you for your suggestion on pressing inwards as you rotate the assembly back into position. My first attempt at installation failed. Then I remembered your suggestion, and that worked on my second attempt. It appears that it is very easy to inadvertently unseat the memory when trying to lock it into position.
 
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petero221

macrumors newbie
May 14, 2010
3
0
I have the 2020 27" iMac with two 4 GB RAM (2667MHz) from Apple installed in slots 1 (Channel A/DiMM1) and 3 (Channel B DiMM1). When I followed the instructions, and installed two OWC 16GB RAM chips (2667MHz) in the free slots (2 and 4), it told me that my Mac had 4 memory slots each of which accepts a 2133 MHz DDR4 memory module - which is clearly incorrect as the slots are 26667MHz! When I installed the 2 x 4GB Apple memory in slots 1 & 2 and the 2 x 16GB OWC in memory slots 3 & 4 it (correctly) told me that my Mac had 4 memory slots each of which accepts a 2667 MHz DDR4 memory module. So now I am completely non-plussed! I haven't use Geekbench or anything but if the Mac thinks it has 2133 MHz memory modules, surely this is a bad thing???? Or is this just a glitch in the Apple OS software and is it running at full speed? I settled with putting the memory in 1&2 and 3&4 respectively but then presumably it doesn't have dual channel support? HELP????
 
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Benz63amg

macrumors 68040
Oct 17, 2010
3,593
600
I have the 2020 27" iMac with two 4 GB RAM (2667MHz) from Apple installed in slots 1 (Channel A/DiMM1) and 3 (Channel B DiMM1). When I followed the instructions, and installed two OWC 16GB RAM chips (2667MHz) in the free slots (2 and 4), it told me that my Mac had 4 memory slots each of which accepts a 2133 MHz DDR4 memory module - which is clearly incorrect as the slots are 26667MHz! When I installed the 2 x 4GB Apple memory in slots 1 & 2 and the 2 x 16GB OWC in memory slots 3 & 4 it (correctly) told me that my Mac had 4 memory slots each of which accepts a 2667 MHz DDR4 memory module. So now I am completely non-plussed! I haven't use Geekbench or anything but if the Mac thinks it has 2133 MHz memory modules, surely this is a bad thing???? Or is this just a glitch in the Apple OS software and is it running at full speed? I settled with putting the memory in 1&2 and 3&4 respectively but then presumably it doesn't have dual channel support? HELP????
You need to update all 4 modules with third party modules of same size and same brand, can’t mix with apple’s own Ram as you lose either speed or dual channel support
 
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petero221

macrumors newbie
May 14, 2010
3
0
You need to update all 4 modules with third party modules of same size and same brand, can’t mix with apple’s own Ram as you lose either speed or dual channel support
On my 2017 27" iMac I happily mixed sizes - kept the two 4GB Apple ones and had 2 x 8GB OWC ones no problems!
 
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wilberforce

macrumors 6502
Aug 15, 2020
359
273
On my 2017 27" iMac I happily mixed sizes - kept the two 4GB Apple ones and had 2 x 8GB OWC ones no problems!
This is very true on all iMacs except the 2020 iMac.

Apple itself has different memory upgrade instructions for the 2020 iMac, stating (for the 2020 iMac only): "For optimal memory performance, DIMMs should be the same capacity, speed, and vendor."
 
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