I have iMac 27" 2019 with 8 Gb DDR4 2666 (2x4GB). Do I need to replace my memory or I can add this memory into empty slots and have 24Gb totally?

Apple Memory Module 16GB DDR4 2666MHz SO-DIMMS (2x8GB)

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  • You can add it in and it should function with the two sets of different size memory cards however it will disable dual channel. Most of the time this should have little to no impact on your performance, however most of the time no single program (plus the OS) will be using more than your base 8gb of ram. Typically it is better to have the same memory types to prevent errors with the way modern programs use memory. If possible just wait until you need them more and get 2-4 of these cards instead to replace the whole array. If you aren't seeing issues of hitting your cap of memory you shouldn't sacrifice speed for more unnecessary ram. You can always close other programs before opening a high need program to ensure you can accommodate it, and the OS is designed to automatically do this in the background as well.

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  • No, you don't have to replace the existing memory cards. The only caveat is the same memory needs to be installed in the coordinated memory slots. IE: in your iMac are 2 4GB cards. 2 similar cards need to be installed in the empty slots (IE: 8GB in each and in series. Not 8GB in one and 4GB in the coordinated slot.) The 2 slots that are occupied are coordinated and the 2 empty slots are coordinated, but between a currently empty and occupied slot is not coordinated. iMac Pro's are different and memory cards in a iMac Pro must be like memory

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