iMac 27" from 2019: Proper order for adding mixed memory modules

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iMac 27" from 2019: Proper order for adding mixed memory modules

There are 4 slots for adding DIMMs of RAM memory. If I have two DIMMs that are 32GB and two that are 8GB, what is the optimal order to load them in the memory bay?

iMac 27″, macOS 14.7

Posted on Oct 31, 2024 8:29 PM

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Answer 1

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den.thed

Level 10

82,594 points

Nov 1, 2024 7:23 AM in response to Tim Purcell

Like all Mac's, the 2019 iMac is more picky about the RAM spec's than about orientation.

If you purchase a pair of compatible modules from either OWC or Crucial and install them in the empty slots, then you should be good to go.

The only iMac that had trouble with the location of mixes modules was the 2020 iMac.

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Answer 2

rkaufmann87

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144,258 points

Oct 31, 2024 9:08 PM in response to Tim Purcell

Simply populate the empty slots with the new RAM. No need to over think adding RAM.

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Answer 3

Tim Purcell Author

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22 points

Oct 31, 2024 9:35 PM in response to Tim Purcell

I had that backwards, matched pairs should be in Banks 0 & 2, and in Banks 1 & 3; ie positions 1 & 3, and positions 2 & 4. There are several benchmarking demos on YT showing that the IO speed drops by half if the arrangement with mixed sizes of DIMMs is not paired in this way in the 2019 iMac. Perhaps newer ones are different.

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Answer 4

Tim Purcell Author

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22 points

Oct 31, 2024 8:57 PM in response to Tim Purcell

I found the answer in this post below. Matched pairs should be used in Banks 0 & 1 and in Banks 2 & 3.

iMac 27" 2019 - correct RAM order? - Apple Community

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