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User profile for user: LIGHTZOFF
LIGHTZOFF Author
User level: Level 1
10 points

imac 2020 27inch compatible ram

Trying to upgrade ram on my new 2020 27inch iMac


I couldn’t find updated docs for installing ram on the new 27inch 2020 iMac and ram compatibility: https://support.apple.com/en-au/HT201191


Am I right to assume that the same Compatible ram specifications for the 2019 27inch iMac would work for the 2020 27inch iMac?


I was also wondering whether this crucial ram would work (it says it is compatible with the 2019 27inch iMac): https://www.crucial.com/memory/ddr4/ct16g4s266m/ct14560735


I have also realised that the required Apple ram specs for upgrade are PC4-21333, however, will PC4-21300 still work as I couldn’t find any ram that was PC4-21333? This thread says it will work, but wanted to confirm: https://discussions.apple.com/thread/251408870


Lastly, I heard that I cannot add additional ram on top of the 8gb that is included with my Mac, is that true?


Thanks

iMac Line (2012 and Later)

Posted on Aug 6, 2020 3:40 PM

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User profile for user: LIGHTZOFF
LIGHTZOFF Author
User level: Level 1
10 points

Posted on Aug 10, 2020 3:55 PM

UPDATE: Thanks for all your replies, this was the first time upgrading RAM on iMac! I ended up going with Crucial CT16G4SFD8266 DDR4-2666 SODIMM 16 GB RAM Memory (I bought 2 individual 16GB sticks because it was cheaper than buying the kit). Although this is not the RAM that is certified by Crucial to work with Mac (CT16G4S266M), I went with CT16G4SFD8266 because it was cheaper and more accessible. After a bit of research, I found out that the only difference between the 2 RAM models is the fact that CT16G4S266M has halogen and lead-free specs to comply with apple environmental standards.


When installing the RAM, all worked fine but I ran into issues with the speed dropping to 2133 MHz (found at Menu : About This Mac Overview). My Setup:


  • Slot 1 - Crucial Memory (16GB)
  • Slot 2 - Apple Memory (4GB) [Did not touch]
  • Slot 3 - Crucial Memory (16GB)
  • Slot 4 - Apple Memory (4GB) [Did not touch]


Essentially, the above configuration dropped my RAM speed to 2133 MHz, so I tried:


  • Slot 1 - Apple Memory (4GB)
  • Slot 2 - Apple Memory (4GB) [Did not touch]
  • Slot 3 - Crucial Memory (16GB)
  • Slot 4 - Crucial Memory (16GB)


The above configuration stopped my Mac from booting so I tried the opposite:


  • Slot 1 - Crucial Memory (16GB)
  • Slot 2 - Crucial Memory (16GB)
  • Slot 3 - Apple Memory (4GB)
  • Slot 4 - Apple Memory (4GB)


The above configuration ended up working and I got my RAM speed to 2667 MHz. This seems to be something specific to the 27inch iMac 2020 model as mentioned by 9to5Mac in this video.


Hope this helps someone in the future.




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User profile for user: LIGHTZOFF
LIGHTZOFF Author
User level: Level 1
10 points

Aug 10, 2020 3:55 PM in response to LIGHTZOFF

UPDATE: Thanks for all your replies, this was the first time upgrading RAM on iMac! I ended up going with Crucial CT16G4SFD8266 DDR4-2666 SODIMM 16 GB RAM Memory (I bought 2 individual 16GB sticks because it was cheaper than buying the kit). Although this is not the RAM that is certified by Crucial to work with Mac (CT16G4S266M), I went with CT16G4SFD8266 because it was cheaper and more accessible. After a bit of research, I found out that the only difference between the 2 RAM models is the fact that CT16G4S266M has halogen and lead-free specs to comply with apple environmental standards.


When installing the RAM, all worked fine but I ran into issues with the speed dropping to 2133 MHz (found at Menu : About This Mac Overview). My Setup:


  • Slot 1 - Crucial Memory (16GB)
  • Slot 2 - Apple Memory (4GB) [Did not touch]
  • Slot 3 - Crucial Memory (16GB)
  • Slot 4 - Apple Memory (4GB) [Did not touch]


Essentially, the above configuration dropped my RAM speed to 2133 MHz, so I tried:


  • Slot 1 - Apple Memory (4GB)
  • Slot 2 - Apple Memory (4GB) [Did not touch]
  • Slot 3 - Crucial Memory (16GB)
  • Slot 4 - Crucial Memory (16GB)


The above configuration stopped my Mac from booting so I tried the opposite:


  • Slot 1 - Crucial Memory (16GB)
  • Slot 2 - Crucial Memory (16GB)
  • Slot 3 - Apple Memory (4GB)
  • Slot 4 - Apple Memory (4GB)


The above configuration ended up working and I got my RAM speed to 2667 MHz. This seems to be something specific to the 27inch iMac 2020 model as mentioned by 9to5Mac in this video.


Hope this helps someone in the future.




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User profile for user: JDee
JDee
User level: Level 5
6,485 points

Aug 6, 2020 3:56 PM in response to VikingOSX

You really need to be super careful about getting the exact type of RAM required. Per this KB article, the 2020 27" iMac requires:


iMac (Retina 5K, 27-inch, 2020) memory specifications for iMac (Retina 5K, 27-inch, 2020),


Memory specifications


This iMac model features Synchronous Dynamic Random-Access Memory (SDRAM) slots on the rear of the computer near the vents with these memory specifications:


Number of memory slots4Base memory8GB (2 x 4GB DIMMs)Maximum memory128GB (4 x 32GB DIMMs)

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

    • PC4-21333
    • Unbuffered
    • Nonparity
    • 260-pin
    • 2666MHz DDR4 SDRAM


Instructions here regarding how to install memory in this model.


There are a number of excellent third party vendors, with detailed videos on how to do it and other detailed information.


Good luck!


-- JDee

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User profile for user: dialabrain
dialabrain
User level: Level 10
126,329 points

Aug 6, 2020 3:55 PM in response to LIGHTZOFF

LIGHTZOFF wrote:

I have also realised that the required Apple ram specs for upgrade are PC4-21333, however, will PC4-21300 still work as I couldn’t find any ram that was PC4-21333? This thread says it will work, but wanted to confirm: https://discussions.apple.com/thread/251408870

As the link states, they are one and the same.

Lastly, I heard that I cannot add additional ram on top of the 8gb that is included with my Mac, is that true?

Not true. See: Install memory in an iMac - Apple Support

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User profile for user: KeyDemon
KeyDemon
User level: Level 1
29 points

Oct 21, 2020 6:15 AM in response to LIGHTZOFF

It definitely helps! Thank you.

I'm purchasing the same memory (just 2x 32GB in kit).


I want to clear up a couple of things though:


  1. AFAIK mixing Apple with any memory (Crucial's "For Mac" as well) will reduce RAM speed to 2133.
  2. The reason why it works in the last configuration (and should in theory work in the second as well) is because you're disabling Dual Channel. You get faster speed, but not dual channel
  3. The reason to purchase kit (and why it sometimes is a tiny bit more expensive) is because they are paired. This is to optimize dual channel compatibility. So if you purchase 2x kits, you should make sure each kit goes in their separate dual channel location (1+3 & 2+4).
  4. PC4-21333 vs PC4-21300 is the exact same thing. It's just a matter of rounding the number (three digits vs five).
  5. If you remove the original Apple RAM and put the Crucial RAM where the Apple RAM was originally, you should get both 2667MHz speed AND dual channel.


Please test number 5 if possible.

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imac 2020 27inch compatible ram

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