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2020 iMac constant crash with 128gb RAM

F

frysteen

macrumors newbie
Original poster
Sep 11, 2011
2
1
I have the a 2020 iMac, 3.6GHz 10 core with AMD Radeon Pro 5700 XT 15GB graphics card.

I purchased 4 x 32 gb 3rd party RAM to put in it - OWC brand - but when I have all 4 sticks in, my iMac constantly crashes.

Happens doing all sorts of things - even minor things some times - but did some tests below.

iMac runs fine with no crashes with various combinations of 3rd party RAM using 2 sticks at a time, so I don't think it is a faulty RAM stick.

- - - - - - - - - -
Test run: create 3000 1 to 1 image preview in Lightroom
No other apps running (also crashed when doing other things, but wanted consistent test for all set-ups).

iMac with 4 x 32gb OWC RAM = crash - ram runs at 2667MHz - tested 3 times, all result in crash.
Crash = entire computer locks up, no mouse movement, computer restarts itself and give crash warning - see screenshots below

iMac with 2 x 32gb OWC RAM = NO crash - ram runs at 2667MHz
iMac with other 2 x 32gb OWC RAM = NO crash - ram runs at 2667MHz
iMac with various different combinations or 2 x 32gb OWC RAM = NO crash - ram runs at 2667MHz
iMac with 2 x 32gb OWC RAM (any combination) and original 2 x 4gb sticks from apple - 4 sticks in at once = NO crash - ram runs at 2133MHz

All RAM test pass when 4 sticks of 32gb of OWC RAM in machine - used Remember app, latest Techtool Pro and Apple Hardware test

Have taken machine to Apple Genius - they found nothing wrong - no real hardware tests run though.
- - - - - - - - - -

Is anyone else having the same issues with 4 x 32BG ram in the new 2020 iMac?

Crash reports attached.
 

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frysteen said:
I have the a 2020 iMac, 3.6GHz 10 core with AMD Radeon Pro 5700 XT 15GB graphics card.

I purchased 4 x 32 gb 3rd party RAM to put in it - OWC brand - but when I have all 4 sticks in, my iMac constantly crashes.

Happens doing all sorts of things - even minor things some times - but did some tests below.

iMac runs fine with no crashes with various combinations of 3rd party RAM using 2 sticks at a time, so I don't think it is a faulty RAM stick.

- - - - - - - - - -
Test run: create 3000 1 to 1 image preview in Lightroom
No other apps running (also crashed when doing other things, but wanted consistent test for all set-ups).

iMac with 4 x 32gb OWC RAM = crash - ram runs at 2667MHz - tested 3 times, all result in crash.
Crash = entire computer locks up, no mouse movement, computer restarts itself and give crash warning - see screenshots below

iMac with 2 x 32gb OWC RAM = NO crash - ram runs at 2667MHz
iMac with other 2 x 32gb OWC RAM = NO crash - ram runs at 2667MHz
iMac with various different combinations or 2 x 32gb OWC RAM = NO crash - ram runs at 2667MHz
iMac with 2 x 32gb OWC RAM (any combination) and original 2 x 4gb sticks from apple - 4 sticks in at once = NO crash - ram runs at 2133MHz

All RAM test pass when 4 sticks of 32gb of OWC RAM in machine - used Remember app, latest Techtool Pro and Apple Hardware test

Have taken machine to Apple Genius - they found nothing wrong - no real hardware tests run though.
- - - - - - - - - -

Is anyone else having the same issues with 4 x 32BG ram in the new 2020 iMac?

Crash reports attached.
Click to expand...
I have an iMac 2020 running 128GB RAM I was using it heavily last week with no problems but this week its crashed on me twice today and once yesterday. The only thing thats changed is me having an external HD plugged in - not sure if this is related. I have removed it and restarted and so far its been ok - weird
 
Last edited:
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mondeotim said:
I have an iMac 2020 running 128GB RAM I was using it heavily last week with no problems but this week its crashed on me twice today and once yesterday. The only thing thats changed is me having an external HD plugged in - not sure if this is related. I have removed it and restarted and so far its been ok - weird
Click to expand...
This also happened to me! I tried usb-c to dp、usb-c hub to external display, when full screen an app, it will show black screen and restart for 120 seconds!!! OMG!!
 
It could be that your modules are dual rank, and the memory controller can't (reliably) run 4x dual rank sticks at the speed apple is trying to run them at.

If Apple don't certify the iMac for 128GB it can be a bit of a crap-shoot depending on how the modules are configured. Dual rank (typically large capacity) modules are harder on the CPU's memory controller than single rank modules (this is why PC motherboards for Ryzen for example have different memory speed support depending on memory configuration).

It may simply be that your individual CPU's memory controller isn't as good as some of them out there and can't do it (and this could be why apple don't certify that configuration on that machine despite it sometimes working).

This may also explain why you are able to run 2 of the sticks in combination with the original RAM at 2133 ok - that isn't as hard on the memory controller. Despite still being 4 sticks in total, the original ram is maybe single rank and (or) lower clocked.
 
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throAU said:
If Apple don't certify the iMac for 128GB it can be a bit of a crap-shoot depending on how the modules are configured
Click to expand...
Apple sells a 128gb configuration. Not sure what modules they use though.
 
bigcat said:
Apple sells a 128gb configuration. Not sure what modules they use though.
Click to expand...

They may be running 2133 modules that are dual-rank and the OP may be running faster modules than that. I'm not sure you can downclock RAM on the mac, i believe it just runs whatever the XMP profile is - which in dual rank may be too fast for the memory controller with the modules used? I could be wrong.
 
throAU said:
They may be running 2133 modules that are dual-rank and the OP may be running faster modules than that. I'm not sure you can downclock RAM on the mac, i believe it just runs whatever the XMP profile is - which in dual rank may be too fast for the memory controller with the modules used? I could be wrong.
Click to expand...
Best I know, imacs ignore XMP profiles and will run at whatever the JEDEC SPD rating of the module is.

Here's some info from Crucial regarding memory ranking though it really only applies to quad rank setups:

"The drawback with higher Ranked modules is that servers sometimes have a limit on how many Ranks they can address. For example, a server with four memory slots may be limited to a total of eight Ranks. This means you can install four Single Ranked modules or four Dual Ranked modules but only two Quad Ranked modules, as installing more would exceed the amount of Ranks that can be addressed."

"Higher rankings can also impact your memory bandwidth, forcing your memory to run at lower speeds when high-ranked parts are present. This trade-off may be required to utilize higher capacities of memory in some systems"
 
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warp9 said:
Best I know, imacs ignore XMP profiles and will run at whatever the JEDEC SPD rating of the module is.
Click to expand...

Hmm maybe it depends. I do know for certain that my MBP 2011 shipped with DDR3-1333 and I upgraded it with DDR3-16xx and it registered the new speed. Maybe it was just looking at the name of the stick, but it shows in about this Mac as 16xx (can't remember if its 1666 or 1600 right now, haven't used it for a while)
 
warp9 said:
"The drawback with higher Ranked modules is that servers sometimes have a limit on how many Ranks they can address. For example, a server with four memory slots may be limited to a total of eight Ranks. This means you can install four Single Ranked modules or four Dual Ranked modules but only two Quad Ranked modules, as installing more would exceed the amount of Ranks that can be addressed."
Click to expand...

This is definitely a thing. recently has been more of a thing on early Ryzen CPUs but does impact intel occasionally as well. Given intel are essentially pushing the same architecture as 5 years ago in Comet lake, it wouldn't surprise me if the memory controller is starting to get pushed with current memory speeds and sizes.
 
warp9 said:
This is completely out of left field but it is real. Sometimes crashes are caused by cosmic rays. These high energy particles can flip bits in the DIMMs as they pass through the atmosphere. It's one of the reasons to get an imac pro because the ECC ram will catch the bad bits. If you have unexplained crashes that aren't repeatable, this could be why.

https://en.wikipedia.org/wiki/Cosmic_ray
https://en.wikipedia.org/wiki/Soft_error#Cosmic_rays_creating_energetic_neutrons_and_protons
Click to expand...
Don't laugh - its absolutely true! You wouldn't believe what cosmic rays can do. Aircraft that fly at high altitudes have to have their electronics shielded from cosmic rays.
 
I seem to have the same kind of issue. I have an imac 2020. I installed 4x32GB of OWC.
when I run Lightroom exports for instance and do a couple other things it tends to crash.
I tried 2x32GB modules seems ok. I switched to the other 2x32, seems ok....
Ill try a memtest tonight
 
I wonder if the RAM wouldnt overheat ...... Strangely, when I keep the RAM door open I dont have crashes. seems.... hard to isolate
 
Everyone keeps talking about the ram, but perhaps one of the slots themselves is bad? OP already said they tried every stick of ram in combinations of 2 with no problems, so that would seem to rule out the ram. What the OP did NOT say is whether they tested all 4 SLOTS when they tried combinations of two sticks only.
 
alright, memtest failed 2 errors detected............. So in my case Ill replace the RAM and test again
 
We own an iMac 17.1 model. Obviously, this is a couple years old.

I'm responding because what you're finding exactly parallels our experience, albeit with a different machine. Exact same problem, although with 4x16Gb RAM, not 4x32Gb.

This problem only started after about a year of using the 16Gb memory modules . Maybe that can be traced to an iMac firmware upgrade - dunno. OWC was very helpful in trying to get this sorted out and exchanged the memory twice for me. They couldn't find anything wrong with the memory that I sent back to them. That's what makes me suspicious of the firmware thing. (Sidenote - This is one of the iMacs that will not update the firmware beyond version 170. Apple has been very uncommunicative about this when asked. Asked by many. This problem may be related - again, dunno.)

Memtest86 failed a bunch of memory combinations. Great test software, though. For me, the original 2x4Gb memory modules passed two days of constant Memtest86 hammering. Never a glitch. Not so for the 16Gb modules.

One additional detail. When the memory glitch started, we were using Sierra. Once this started, something on the internal SSD got corrupted. None of the usual solutions would work, up to and including a Command-R boot and a complete replacement of the operating system. The Apple store people were most helpful, and said that they could do a low level update, which would wipe the drive entirely as if factory new. Would we like Mojave or Catalina? We chose Mojave. That didn't help with the goofy memory situation, but so far things have worked well. I'd blame this all on our iMac sample, except so many others have seen the exact same problem.

There's been loads of forum posts on this issue, here and elsewhere.

Quick summary:

You can try switching the sticks to different slots. That sometimes works.

You can try putting the RAM that originally came with the iMac back in and mixing the new RAM in open slots.

The only combination I've found to work is the original 2x4Gb that came with the iMac in combination with 2x16Gb that we bought after. Yeah - 40Gb. Only two of the 16Gb modules work in that combination.

If we have more problems, I might go back to using 4x8Gb memory modules. That worked for a couple years without a problem. Maybe the moral of the story is that some of the hardware (and maybe software) designs are optimized for the OEM memory, and using aftermarket memory, no matter good, doesn't always work. I doubt Apple tests for a variety of memory suppliers. Or, cares to. So, if timing is marginal to begin with, installing memory that sits on the other side of the timing spec fails. Why this should suddenly happen after a long period beats the heck out me.

This all makes me want to upgrade the operating system or buy new Apple hardware oh so much. Right...
 
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I have the 27" iMac 2020 and purchased OWC 4X16Gb modules. My unit froze two times within two weeks of use using Safari. I had to unplug the desktop to reset the computer. It hasn't happened lately, but I don't use it every day either.
I've had this Apple for about 4 weeks now. I'm a PC convert - new to apple.
 
The common denominator to everyone in this thread with issues, is 4 modules of OWC memory. This really looks like a manufacturing defect or oversight on the part of OWC.
 
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