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Memory upgrades for 2019 Mac Pro: "largest to smallest" capacity

Memory upgrades for 2019 Mac Pro:


It should read "largest to smallest" capacity in the section titled "Installing DIMMs of mixed capacities".

Mac Pro, macOS 10.15

Posted on Dec 20, 2019 1:12 PM

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6 replies

Dec 20, 2019 2:08 PM in response to Grant Bennet-Alder

https://support.apple.com/en-us/HT210103?cid=macOS_UI_Memory_article_HT210103


How to install DIMMs of mixed capacities

  1. Find out which slots to use for your DIMM configuration.
  2. Starting with the lowest capacity pair of DIMMs, install your DIMMs in identical pairs from smallest to largest capacity in order of the memory channels:


"smallest to largest" is incorrect. it should read "largest to smallest"



Dec 25, 2019 2:14 AM in response to Grant Bennet-Alder

I can see PuckettM's point. On that URL - you see the wording in the section "Installing DIMMs of mixed capacities" stating that "starting with the lowest capacity... install from smallest to largest capacity in order of the memory channels". To me, that would imply that the lowest capacity memory goes in memory channel 1 (slots 5 to 8), and the highest capacity DIMMs go in the higher numbered memory channels.


But scroll down to the "Verify your memory" section and look at the screenshot where 8Gb and 32Gb DIMMs are mixed. The 32Gb pairs go in slots 5 to 8, which is memory channel 1 and slots 3 and 10 (memory channel 2). The 8Gb DIMMs go in memory channels 3 and 4. That would not represent installing "from smallest to largest capacity in order of the memory channels".


It seems as if you'd be as well putting them in whichever order you like and then letting macOS tell you where they should go!

Dec 25, 2019 8:35 AM in response to Karen

There is a long history of always installing highest density DIMMs in the "first" slots.


There has been another User reporting that this lowest to highest language actually does not work in practice.


I have asked Moderators to have this escalated to be clarified. Apple corporate shuts down for end-of-year, so it may be a while before more concrete information is available.

Memory upgrades for 2019 Mac Pro: "largest to smallest" capacity

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