Yet Another Complication Upgrading Ram on Retina 5K, 27" 2020 iMac

[jordii]

I read all the threads before installing a kit of 2x16GB Crucial RAM modules (DDR4 2666MHz, CT2K16G4S266M) into my iMac20,1 (Retina 5K, 27-inch, 2020 3.3 GHz 6-Core Intel Core i5).

I discarded Apple's stock 2x4GB modules, and installed the new ones in their place, slots 2 and 4. But I'm not getting 2667MHz.

"About this Mac" shows "32 GB 2133 MHz DDR4" and below is a screenshot from system report. The modules label do specify 2666.

 

[Fishrrman]

Try putting them BOTH on Channel A.

 

[jordii]

My understanding was that that's the move for previous model iMacs, but not the 2020 5K. Also, Apple put their modules in 2 and 4!

thanks, I'll try though

 

[Sully]

My understanding was that that's the move for previous model iMacs, but not the 2020 5K. Also, Apple put their modules in 2 and 4!

thanks, I'll try though

Just an FYI, I have the same computer and installed these exact RAM modules upon purchase. Mine are in slots 2 and 4 and they both show 2666.

Maybe return these modules and try new ones?

 

[jordii]

Just an FYI, I have the same computer and installed these exact RAM modules upon purchase. Mine are in slots 2 and 4 and they both show 2666.

Maybe return these modules and try new ones?

Yeah. I'm starting to settle into that conclusion. Thanks. Though super odd that both are doing this.

Hey, would you mind screenshotting your system report window? I'm curious to compare the details.

 

[Sully]

Yeah. I'm starting to settle into that conclusion. Thanks. Though super odd that both are doing this.

Hey, would you mind screenshotting your system report window? I'm curious to compare the details.

 

[jordii]

Many thanks, I appreciate it, but could you possibly shoot the memory system report?

About This Mac > More Info... > General > [scroll down to bottom] System Report... > Memory

The bottom pane has all the part and manufacturing numbers, which would show if I'm using the exact same (and correct) modules (i.e. Crucial didn't mis-label mine).

For comparison, here's my memory system report:

 

[HobeSoundDarryl]

OP, while it probably won't matter, pull them and swap the slots (the one that is in slot 4 goes into slot 2 and vice versa) when you put them back in. A simple re-seat might make a difference. This swap shouldn't make any difference but it's easy enough to try.

And I'd go ahead and try slots 1 & 3 too with that RAM too. That might force the system to see it as NEW RAM. If that perhaps gets it showing at full speed, you could swap it back and check again. If lower in 2 & 4, I start thinking that perhaps something needs to be zapped. There's 2 or 3 things you can zap by holding down select keys on the keyboard when turning on an iMac and that might apply... but that's towards wildest guess as it's been a LONG time since I've had to do that kind of thing.

Also see this thread about the same issue with many potential resolutions.

And here's 22 pages of posts that claim to actually resolve the issue... and references within it talking about several other threads on this matter.

 

[jordii]

OP, while it probably won't matter, pull them and swap the slots (the one that is in slot 4 goes into slot 2 and vice versa) when you put them back in. A simple re-seat might make a difference. This swap shouldn't make any difference but it's easy enough to try.

And I'd go ahead and try slots 1 & 3 too with that RAM too. That might force the system to see it as NEW RAM. If that perhaps gets it showing at full speed, you could swap it back and check again. If lower in 2 & 4, I start thinking that perhaps something needs to be zapped. There's 2 or 3 things you can zap by holding down select keys on the keyboard when turning on an iMac and that might apply... but that's towards wildest guess as it's been a LONG time since I've had to do that kind of thing.

Remember when "Zap the Pram!" was the answer for everything?

 

[Sully]

Many thanks, I appreciate it, but could you possibly shoot the memory system report?

About This Mac > More Info... > General > [scroll down to bottom] System Report... > Memory

The bottom pane has all the part and manufacturing numbers, which would show if I'm using the exact same (and correct) modules (i.e. Crucial didn't mis-label mine).

For comparison, here's my memory system report:
View attachment 2341854

Sorry. I used OWC memory for this upgrade. I recently used Crucial for another device and confused the two.

Maybe you should return the Crucial and get OWC RAM. lol!

My apologies for the mistake. Good luck.

 

[wilberforce]

I have the same Crucial modules in the same slots and they work fine at 2667 MHz

 

[jordii]

Sully: No sweat. Thanks!

wilberforce: Thanks! Weird, huh?

HobeSoundDarryl: Glad I caught your edit! Why is it every simple thing I try to do turns into a rabbit hole of pain and confusion?
🤣

 

[jordii]

OP, while it probably won't matter, pull them and swap the slots (the one that is in slot 4 goes into slot 2 and vice versa) when you put them back in.

And I'd go ahead and try slots 1 & 3 too with that RAM too.

No joy from either.

It's hard to suspect bad RAM, given that both modules behave the same. I'll chat with Crucial tomorrow, but don't have much hope.

 

[Fishrrman]

Once again...

Did you at least try to put both DIMMs into a "single channel"?
(i.e., slot 1 and 2) ?

 

[jordii]

It doesn't help

 

[MacMore]

My guess is that your RAM is unmatched. If you put the two Apple RAM chips in slots 1 and 2, and the Crucial RAM in solots 3 and 4 it should report correctly. Generally you should fill your RAM slots with matched pairs.

If that doesn't work then return the RAM as faulty and get a refund.

 

[jordii]

My guess is that your RAM is unmatched. If you put the two Apple RAM chips in slots 1 and 2, and the Crucial RAM in solots 3 and 4 it should report correctly. Generally you should fill your RAM slots with matched pairs.

If that doesn't work then return the RAM as faulty and get a refund.

I bought the two Crucial modules as a kit, and their serial numbers confirm by being consecutive (per my Mac's system info, see screenshot in OP)

 

[MacMore]

I bought the two Crucial modules as a kit, and their serial numbers confirm by being consecutive (per my Mac's system info, see screenshot in OP)

None of this matters if they are not in the same channels.... which you have completely overlooked by your response to me.

Put the Apple RAM in one channel an the Crucial RAM in the other... Mismatched RAM can cause this issue. Or just send it back and get your RAM from OWC who use the same chips as Apple.

 

[jordii]

I tried it and it didn't help. I didn't think I owed you a blow-by-blow.

I was aware that returning the modules was an option, but thanks for the fatherly advice.

Finally, OWC = Apple is incorrect. Apple sources widely.

 

[saudor]

Once again...

Did you at least try to put both DIMMs into a "single channel"?
(i.e., slot 1 and 2) ?

Don't do this. Even if it worked, you're now running the memory in single channel mode. You're better off running them as 2133 and in dual channel

Anyways this is commonly seen in RAM kits. For prebuilts or locked down mobos, the JEDEC spec needs to be 2666 (many kits are 2133 and need to be overclocked via XMP, etc to hit the speeds on the sticker). However, the one OP has a mac label on it so in theory should be 2666 (however, i can't find this in the specs except for that other poster claiming it works at 2666 in their mac)

I'd probably send it back and get another kit, preferably one that mentions the JEDEC spec of 2666

 

[jordii]

Don't do this. Even if it worked, you're now running the memory in single channel mode. You're better off running them as 2133 and in dual channel

Anyways this is commonly seen in RAM kits. For prebuilts or locked down mobos, the JEDEC spec needs to be 2666 (many kits are 2133 and need to be overclocked via XMP, etc to hit the speeds on the sticker). However, the one OP has a mac label on it so in theory should be 2666 (however, i can't find this in the specs except for that other poster claiming it works at 2666 in their mac)

I'd probably send it back and get another kit, preferably one that mentions the JEDEC spec of 2666

As I mentioned above, using contiguous slots (e.g. 1 and 2) works for older iMacs, so that's likely the source of the suggestion. The 2020s are weird, which means users of older iMacs unwittingly contributing FUD.

As for the JEDEC spec, Idunno. So many people are using Crucial memory for this purpose (not just the person who dropped in and kindly offered his screenshot) that this can't possibly be the expected result. In fact, after reading several hundred pages of tortured discussion, I haven't seen anyone report exactly this result (i.e. after REMOVING stock modules, and using the correct - i.e. 1/3 or 2/4 - slots, and installing a kit rather than two separately-bought modules).

But, yeah, I'm definitely returning it....though, in the end, 2133 is confessedly plenty fast enough for my work flow.

 

[Fishrrman]

If you take the 3rd-party RAM out, and put the Apple RAM back in, do you get the full speed then?

 

[gilby101]

The Mac will be so much faster with 32GB RAM compared with 8GB. You could decide to accept as is and not worry about the 2133 or 2666 issue. So many people have gone round and round in circles with the 2020 iMac. (Glad, from RAM point of view, that I have a 2019 iMac.)

 

[jordii]

The Mac will be so much faster with 32GB RAM compared with 8GB. You could decide to accept as is and not worry about the 2133 or 2666 issue. So many people have gone round and round in circles with the 2020 iMac. (Glad, from RAM point of view, that I have a 2019 iMac.)

Yeah, I confess, above, that 2133 is more than fast enough. But I spent the money on the ram, so want to get it right.

 

[Andrey84]

Try putting them BOTH on Channel A.

Won't the OP lose the dual-channel speed benefit then?