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pldelisle

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Since many people were asking which RAM modules they could use to upgrade the 2019 or 2020 iMac, here are once and for all the compatible memory modules for both models. Feel free to add any kits you personally tested.



Memory upgrade compatibility list for iMac 2019-2020


Compatible Crucial part numbers (compatibility verified and confirmed on manufacturer's website):


See the 2666 MT/s modules in Crucial Memory for Mac Systems

Compatible Crucial part numbers (Tested from Forum users):

Crucial CT2K32G4SFD8266 64GB Kit (32GB x2)


Compatible Kingston part numbers (compatibility verified and confirmed on manufacturer's website):

Part numberCapacityAmazon USAmazon CanadaAmazon UK
KCP426SS6/4 1 x 4 GBBuy nowBuy nowBuy now
KCP426SS8/8 1 x 8 GBBuy nowBuy nowBuy now
KCP426SS8/161 x 16 GBN/AN/AN/A
KCP426SD8/16 1 x 16 GBBuy nowBuy nowBuy now
KCP426SD8/321 x 32 GBN/ABuy nowBuy now


Compatible OWC part numbers (compatibility verified and confirmed on manufacturer's website):



Compatible Samsung part numbers (compatibility cannot be verified on manufacturer's website):

Part numberCapacityAmazon USAmazon CanadaAmazon UK
M471A5244CB0-CTD1 x 4 GBN/AN/ABuy now
M471A1K43CB1-CTD1 x 8 GBBuy nowBuy nowBuy now
M471A1K43DB1-CTD1 x 8 GBN/AN/AN/A
M471A2K43CB1-CTD1 x 16 GBBuy nowBuy nowN/ABuy now
M471A2K43DB1-CTD1 x 16 GBN/AN/AN/A
M471A4G43MB1-CTD1 x 32 GBBuy nowBuy nowBuy now


Compatible SK Hynix part numbers (compatibility cannot be verified on manufacturer's website):
* Not confirmed, but seems the only other model available on SK Hynix website. Shares same 1Gx64 or 2Gx64 organization spec as the original Apple RAM.

iMac 2019-2020 needs :
  • PC4-21333
  • Unbuffered
  • Nonparity
  • 260-pin DR (Dual Ranked) or SR (Single Ranked)
  • 2666MHz
  • CL19
  • 1.2v
  • Source : Install memory in an iMac.


See Installation instructions upon receiving your RAM module(s).

Please note that many people on this forum experienced problems when mixing genuine Apple RAM with third party RAM. It might not be possible to mix your genuine Apple RAM with the modules listed above without impacting stability and performance. Memory configuration with 2 or 4 memory modules coming from the same third party vendor is strongly recommended.

For troubleshooting RAM, please refer to this thread Memory upgrade troubleshooting in 2020 27-inch iMacs

Rules of thumb :

  1. Do not mix RAM modules with different capacity/speed/manufacturer. A OWC memory kit with Hynix ICs won't work with an OWC memory kit with Micron ICs, even if they are "For Mac", with the same speed, timings, comes from the same manufacturer, and other specs.
  2. If you chose to upgrade to, for example, 2x32 GB, and have 2 memory slots free for future upgrade, chose Crucial RAM. It's the only RAM brand which has a unique ICs manufacturer which is Micron. Kingston usually have a locked BOM for ValueRAM Server RAM, but I can't find the same information for Mac RAM. Crucial is the only 100% certified compatible RAM and guarantee that it will work in the future when adding a second kit.
  3. No experiment show that mixing Apple stock RAM with aftermarket RAM listed above is correctly operating at full speed and in dual channel. Don't mix Apple RAM with aftermarket RAM.
  4. Memory must be installed in slot 1-3 and 2-4 when in kit of 2 SODIMM modules. If all 4 SODIMM are populated, make sure all ICs are coming from the same manufacturer. If not, dual channel is lost.
 
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noir_et_noir

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Aug 6, 2020
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What about the Samsung M471A4G43MB1-CTD? 32GB stick? Specs all fall in line and have plenty of success history through here and Reddit especially back with the last Mac Mini release.
(Link: https://www.samsung.com/semiconductor/dram/module/M471A4G43MB1-CTD/)

Currently only $120 (at memory.net) for 32GB stick -- $480 if you want to max out to 128GB.


I feel like your warning of anything other than what's listed above unfairly rules out other viable producers including Samsung and Hynix RAM.

Edit: See it listed now 👍🏼
 
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pldelisle

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What’s the difference between
The first is listed in Crucial Memory for Mac Systems, the second is not. But they share the same specs, voltage, timing, frequency, density, everything...

I think Crucial hasn't created a 64 GB kit yet specifically for the iMac 2020. They have the part listed in official documentation but the kit is still not listed for sale, probably because they want to have an iMac to test it. The CT2K32G4S266M will probably be on sale soon once Crucial got their hand on the iMac 2020.
 
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cadamwil

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Mar 7, 2012
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Question, the processor in the top spec (standard proc) 27" iMac is an Intel® Core™ i7-10700K, correct? If so, why wouldn't it use DDR4-23400 (2933 Mhz) as listed in the processor specifications instead of the DDR4-21333 (2666 Mhz)? Isn't apple slowing it down a bit using sub top speed ram?


 
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pldelisle

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Question, the processor in the top spec (standard proc) 27" iMac is an Intel® Core™ i7-10700K, correct? If so, why wouldn't it use DDR4-23400 (2933 Mhz) as listed in the processor specifications instead of the DDR4-21333 (2666 Mhz)? Isn't apple slowing it down a bit using sub top speed ram?


Yeah the CPU support higher clock speeds. I don’t know why Apple is using 2666MHz on this 2020 iMac. When writing this post I followed Apple official specs. Someone will have to try faster RAM if it works but I doubt. BIOS will likely downclock the RAM to the supported 2666MHz.
 

Moshe1010

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Jun 27, 2010
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Question, the processor in the top spec (standard proc) 27" iMac is an Intel® Core™ i7-10700K, correct? If so, why wouldn't it use DDR4-23400 (2933 Mhz) as listed in the processor specifications instead of the DDR4-21333 (2666 Mhz)? Isn't apple slowing it down a bit using sub top speed ram?


Probably due to heat. i7 and def. i9 are hot potatoes, especially in the outdated iMac infrastructure
 

Fernandez21

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Jun 16, 2010
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What are peoples thoughts on Samsung RAM? Looking at getting 2 of these for $250 for 64gb total while leaving the other 2 slots open for future upgrade to 128gb, or would it be ok to leave the 8gb from apple in there and have 72gb?

c42b9c7af600893f23a9cc8f77f9399e.jpg
 
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pldelisle

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pldelisle

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May 4, 2020
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Montreal, Quebec, Canada
What are peoples thoughts on Samsung RAM? Looking at getting 2 of these for $250 for 64gb total while leaving the other 2 slots open for future upgrade to 128gb, or would it be ok to leave the 8gb from apple in there and have 72gb?

c42b9c7af600893f23a9cc8f77f9399e.jpg

As long as you get the modules listed in first post it’s fine.
Samsung makes memory more for OEMs and less for retail. That’s why almost nobody will have thoughts about Samsung, but it’s still a good memory brand. Good point of it is that they use their own DRAM chip, Samsung being a DRAM chip maker. So the whole module is Samsung made, just like Crucial which is Micron. Kingston is usually a mix of Hynix and Micron depending on which costs less when they order a batch of DRAM chips.
 
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CheesePuff

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Sep 3, 2008
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I didn’t even know they were still in business. Poor reliability back when I was building Pcs 7-8 years ago. Might have changed by now.

They also make 'Mac' specific versions of their RAM like Crucial does, but the specs are identical, so going to try these. Worst case is I return them and pay $6 more per stick x4 for the Crucial brand.
 

NewUsername

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Aug 20, 2019
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Noob question. I wanted to order the Crucial memory, but I noticed a module of 16GB would cost me €70, whereas a 2x16GB kit would cost me €145. I suppose I should just order two separate models then and save €5? Or is there any difference between two separate 16GB modules and a kit of 2x16GB?
 

pldelisle

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Noob question. I wanted to order the Crucial memory, but I noticed a module of 16GB would cost me €70, whereas a 2x16GB kit would cost me €145. I suppose I should just order two separate models then and save €5? Or is there any difference between two separate 16GB modules and a kit of 2x16GB?
Generally the RAM sold in kit is tested in kit. So both modules are "certified" to work perfectly together.

It's always better to buy as a kit.
 

NewUsername

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Aug 20, 2019
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Generally the RAM sold in kit is tested in kit. So both modules are "certified" to work perfectly together.

It's always better to buy as a kit.
Yes, but in the case of Crucial even the model numbers are identical. So what I mean is: is there a difference between buying CT2K16G4S266M or between buying CT16G4S266M two times?
 

pldelisle

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Yes, but in the case of Crucial even the model numbers are identical. So what I mean is: is there a difference between buying CT2K16G4S266M or between buying CT16G4S266M two times?
Re-read my post.

CT16G4S266M is a single module.
CT2K16G4S266M is a kit with 2x CT16G4S266M modules.

The CT2K16G4S266M is tested with 2x CT16G4S266M to perfectly work together. That's what I said.

For a 5$ difference, buy CT2K16G4S266M. Or even better, by 2x CT2K16G4S266M ;)
 

KrazyKanuck

macrumors regular
Aug 8, 2020
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Yes, but in the case of Crucial even the model numbers are identical. So what I mean is: is there a difference between buying CT2K16G4S266M or between buying CT16G4S266M two times?
Well, I bought two pairs of the same Crucial 8GB two days apart from the same retailer and all four sticks are cooperating. But that is four "identical" sticks purchased in pairs over the space of two days.
 
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