Memory upgrade troubleshooting in 2020 27-inch iMacs

[filmgirl]

Hello guys, i have 2020 iMac

I have 2x4gb Hynix, and 2x4gb Micron ram, (16gb total)

if I put Micron-Hynix-Micron-Hynix the speed downgrades to 2133

Do I need to put Micron-Micron-Hynix-Hynix to keep 2666? Will I keep dual channel with this setup?

Thanks for answer friends!

You will not keep dual channel and full speed with this setup.Your options are to run in dual channel and lower speed (recommended) or faster speeds and single channel (not).

If you want dual channel and full speed you’ll need to get another kit of RAM that matches the additional 8GB you bought separately.

 

[filmgirl]

Good catch! I don't recall that text being on the site earlier. If you look at the bottom of the page it says published on "September 02, 2020". It also appears that the text "For optimal memory performance, DIMMs should be the same capacity, speed, and vendor" is unique to only the 2020 iMacs. Hmm...

Install memory in an iMac - Apple Support (CA)

Get memory specifications and learn how to install memory in iMac computers.

support.apple.com

There is also this paragraph specific to the 2020 iMac:

iMac (Retina 5K, 27-inch, 2020) DIMMs have a notch on the bottom, slightly left of the middle. If your DIMMs are mixed in capacity, minimize the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4) when possible.

 

[Kotomoto]

You will not keep dual channel and full speed with this setup.Your options are to run in dual channel and lower speed (recommended) or faster speeds and single channel (not).

If you want dual channel and full speed you’ll need to get another kit of RAM that matches the additional 8GB you bought separately.

Okey thanks!
Think to buy 2x16 then, from Amazon. And keep 32gb at 2666 speed.
Best option imo.

 

[Lisse]

By now it seems the horse is far beyond dead, but should there be a need for an additional beat:

Here are the screen captures from the Apple Support page. One has a date of August 5, 2020. The other has a date of September 2, 2020.

I wonder if knowing this before purchase would have made any difference to those who bought one.

 

[mikehalloran]

By now it seems the horse is far beyond dead, but should there be a need for an additional beat:

Here are the screen captures from the Apple Support page. One has a date of August 5, 2020. The other has a date of September 2, 2020.

I wonder if knowing this before purchase would have made any difference to those who bought one.

Anyone who read this thread knew this was coming. In fact, I predicted that Apple would post such a support update a couple of weeks ago.

It certainly makes no difference to me as to whether or not I would have bought my wife's 2020 or when or would have changed my RAM purchase for her machine.

In the real world, this won't matter to most users as they will not notice any difference in performance. None of my testing has revealed any. Since Geekbench doesn't measure real world performance, I don't use it.

 

[filmgirl]

By now it seems the horse is far beyond dead, but should there be a need for an additional beat:

Here are the screen captures from the Apple Support page. One has a date of August 5, 2020. The other has a date of September 2, 2020.

I wonder if knowing this before purchase would have made any difference to those who bought one.

I doubt it. The only thing it really changes is whether you’re expecting to use that 8GB or if you should adjust your budget to get a larger RAM kit. Even then, the cost of a bigger RAM kit is still way less expensive than what Apple charges to go to more RAM. Apple wants another $200 to go to 16GB. A 16GB kit from Crucial is $75 so even if you have to write off the included RAM, it’s still over 50% cheaper.

I’m just glad Apple clarified what we’ve all found in testing.

 

[pmiles]

There is also this paragraph specific to the 2020 iMac:

So does this mean Apple is telling users to put say 2 8GBs in slots 1&2 and 2 16GBs in slots 3&4 or 2 8GBs of Apple RAM in slots 1&2 and 2 8GBs of Crucial RAM in slots 3&4 because it is mixed?

That the only way to get dual channel support is to populate all 4 slots (if maxing out the system) with the same exact RAM?

LOL, can we buy a new iMac sans any memory?

 

[pldelisle]

LOL, can we buy a new iMac sans any memory?

No.

That the only way to get dual channel support is to populate all 4 slots (if maxing out the system) with the same exact RAM?

Or the exact same RAM in slot 1 & 3.

 

[TheTrueZoltan!]

I just ordered a 2x32 GB set from Crucial. Will order a second set soon to max out the iMac‘s RAM capacity. I don‘t really need the full 128 GB right now, but in two or three years... who knows? And perhaps I am not able to get the same set from Crucial anymore then?! So I guess it‘s better to max it out now to be sure I get two sets that work together nicely.

 

[mikehalloran]

I just ordered a 2x32 GB set from Crucial. Will order a second set soon to max out the iMac‘s RAM capacity. I don‘t really need the full 128 GB right now, but in two or three years... who knows? And perhaps I am not able to get the same set from Crucial anymore then?! So I guess it‘s better to max it out now to be sure I get two sets that work together nicely.

There are certainly worse ways to approach this.

 

[pldelisle]

I just ordered a 2x32 GB set from Crucial. Will order a second set soon to max out the iMac‘s RAM capacity. I don‘t really need the full 128 GB right now, but in two or three years... who knows? And perhaps I am not able to get the same set from Crucial anymore then?! So I guess it‘s better to max it out now to be sure I get two sets that work together nicely.

Crucial uses Micron-only DRAM chips. It will work in the future. It’s not OWC that buys DRAM chip from both Hynix and Micron and you can‘t know on which batch you are going to fall.

 

[Gary Irwin]

WTF?

Added Crucial 2x16GB CT2K16G48FD8266 SODIMM's (from Amazon.ca) to my new 2020 27" i7 iMac. Integrating them with Apples OEM cause the computer to drop from 2666Mhz to 2133 -- commonly reported issue. So pulled the OEM memory and went solely with Crucial in slots 1 & 3. System back at 2666, Geekbench at 9000. All is good. So ordered an additional 2x16GB CT2K16G48FD8266 and inserted them into slots 2 & 4. iMac reports 32GB @2133Mhz and Geekbench drops to 8400?

I triple checked the mem packages they are EXACTLY the same -- ordered 1 day apart.

FALSE ALARM -- different SODIMMs in identical packages. Go figure.

 

[pldelisle]

WTF?

Added Crucial 2x16GB CT2K16G48FD8266 SODIMM's (from Amazon.ca) to my new 2020 27" i7 iMac. Integrating them with Apples OEM cause the computer to drop from 2666Mhz to 2133 -- commonly reported issue. So pulled the OEM memory and went solely with Crucial in slots 1 & 3. System back at 2666, Geekbench at 9000. All is good. So ordered an additional 2x16GB CT2K16G48FD8266 and inserted them into slots 2 & 4. iMac reports 32GB @2133Mhz and Geekbench drops to 8400?

I triple checked the mem packages they are EXACTLY the same.

Only thing I can see is that Apple says PC4-21333 recommended, but Crucial's site indicates CT2K16G48FD8266 is PC4-21300?

What am I missing?

If there is a kit that should work flawlessly is this one. Same DRAM manufacturer, same spec... weird. Maybe try reorder them? It shouldn’t be a problem, the modules are identical.

 

[Gary Irwin]

If there is a kit that should work flawlessly is this one. Same DRAM manufacturer, same spec... weird. Maybe try reorder them? It shouldn’t be a problem, the modules are identical.

Starting to wonder if I should just spurge on 2x32GB modules and call it a day.

 

[quagmire]

WTF?

Added Crucial 2x16GB CT2K16G48FD8266 SODIMM's (from Amazon.ca) to my new 2020 27" i7 iMac. Integrating them with Apples OEM cause the computer to drop from 2666Mhz to 2133 -- commonly reported issue. So pulled the OEM memory and went solely with Crucial in slots 1 & 3. System back at 2666, Geekbench at 9000. All is good. So ordered an additional 2x16GB CT2K16G48FD8266 and inserted them into slots 2 & 4. iMac reports 32GB @2133Mhz and Geekbench drops to 8400?

I triple checked the mem packages they are EXACTLY the same -- ordered 1 day apart.

Only thing I can see is that Apple says PC4-21333 recommended, but Crucial's site indicates CT2K16G48FD8266 is PC4-21300?

What am I missing?

Put the first set of crucial RAM in slots 1 and 2. Then put the new Crucial RAM in slots 3 and 4. That should get it back to full speed and since it is all the same RAM size still maintain dual channel.

Though am I reading it right that the iMac sees 4x16 GB as 32 GB total?

 

[Gary Irwin]

Ok, sorry for the false alarm. I pulled the SODIMM's and the labels are completely different. The outside of the packages they came in are identical in every way, same specs, colour size etc etc. but it's obvious the modules are not the same. Don't know who messed up but they're on their way back to Amazon now. I'll be ordering 2x32GB.

 

[mikehalloran]

Ok, sorry for the false alarm. I pulled the SODIMM's and the labels are completely different. The outside of the packages they came in are identical in every way, same specs, colour size etc etc. but it's obvious the modules are not the same. Don't know who messed up but they're on their way back to Amazon now. I'll be ordering 2x32GB.

Thanks for posting the update.

So now you know that you didn't get identical sticks — even though they did install and the Mac fired up.

Fortunately, being Amazon, you can return.

This issue is hardly a month old and Apple updated their support page two days ago.

Although Crucial & OWC are by now fully aware of this, it's a good idea to assume that the rest of the world will not catch up for awhile

 

[Gary Irwin]

Although Crucial & OWC are by now fully aware of this, it's a good idea to assume that the rest of the world will not catch up for awhile

I also see Crucial has released memory specifically for Mac's. Probably the safest way to go considering how fussy the new iMacs are.

 

[pldelisle]

I also see Crucial has released memory specifically for Mac's. Probably the safest way to go considering how fussy the new iMacs are.

From what I know, the difference is only between materials used for the PCB to meet Apple’s environmental policies.
But yes. When possible, always take certified RAM for Mac. And Crucial is the only manufacturer which can both certify the compatibility for mac and guarantee full speed and performance if you keep 2 slots free for future upgrade. Crucial will always use Micron chips with the same specs contrary to OWC which can be a mix of Micron and Hynix depending on which they buy when they need ICs. Kingston, while having locked BOM for server RAM, doesn’t mention the same for mac memory on their website.

Samsung doesn’t have a memory configurator to certify the compatibility of their RAM for mac but will also guarantee a future upgradability since they make their own DRAM chips.

 

[AZREOSpecialist]

You don't need Crucial RAM. I bought no-name 32 GB sticks for 2019 iMac on NewEgg and am getting 2666 MHz w/ 64 GB. NO issues.

 

[mikehalloran]

You don't need Crucial RAM. I bought no-name 32 GB sticks for 2019 iMac on NewEgg and am getting 2666 MHz w/ 64 GB. NO issues.

You’re missing the point.

 

[pldelisle]

You don't need Crucial RAM. I bought no-name 32 GB sticks for 2019 iMac on NewEgg and am getting 2666 MHz w/ 64 GB. NO issues.

I personally don’t like to put no-name memory inside a 4000$ computer.

 

[ADGrant]

I personally don’t like to put no-name memory inside a 4000$ computer.

Agreed. I always insist on OEM parts in my car too (absent a very good reason not too).

 

[AZREOSpecialist]

You’re missing the point.

Being that you need to use all of the same size and type of RAM sticks to get optimal performance? Of course. But all the mention of Crucial around here sounds like an advertisement. I'm sure they're great, but more expensive than equally good memory that can be obtained elsewhere.

 

[esdonohoo]

I have two of what should be identical Crucial 2x16 pairs that behave differently depending how they are installed. I'm wondering what's going on.

I ordered the CT2K16G4S266M from Amazon at the same time I ordered the iMac. When it arrived, I replaced the 2 4G sticks in slots 2 and 4 with the Crucial kit and everything looked great. Reported speed of 2667 MHz.

Then I saw a good price on the same Crucial kit from Newegg and decided to just go ahead and populate the other two slots. I ordered the same 32G kit but actually received two individual sticks with the part number CT16G4S266M. From what I could tell on the Crucial site, these are the same DIMMS as in the 2x16 kit so I tried them in slots 1 and 3.

The speeds dropped down to 2133. I swapped them around so the original pair is in slots 1/2 and the new pair in slots 3/4. Now reporting 2667 for all four.

All four sticks report the same major part number, CT2K16G4S266M, but report different manufacturers and minor part numbers. Would that be sufficient to cause the drop to 2133 when they are interleaved across channels despite both pairs being Crucial with identical specs and speed? This is baffling. Am I truly getting dual-channel here when all four are reporting 2667?