I have an iMac Retina 5K (27-inch, Late 2014) with 8 GB of RAM (2 * 4 GB 1600 MHz DDR3 memory modules). There are 2 memory slots free/available, and I want to add RAM to these two slots.

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My question is - Am I required to add only 4 GB memory sticks into these empty slots, or is it perfectly fine if I add a higher capacity RAM (8 GB sticks) in these empty slots?

I don't want to swap out the existing 4 GB RAM sticks. I want to keep these two as is, and add two more RAM sticks of 8 GB each.

I want to do this if I can be perfectly sure this works, and does not affect the system performance/reliability in any way.

I reached out to Apple customer support, and the customer service agent told me he wasn't sure, and that I should just stick to 4 GB uniformly across all slots.

Any of you good people have tried this already and have some advice?


  • perfectly fine - I have 2's, 4's & 8's in mine [in pairs, over 8 slots] As Matthieu says, check they're otherwise the same type
    – Tetsujin
    Commented Mar 9, 2015 at 12:03

3 Answers 3


Yes, like on every other computer you can mix the ram sizes.

Though watch for the frequences (they have to be at same or higher) and the compatibilites.


The newer imacs support dual channel what means that tou can have 2 different sorts of ram memory. But make sure that there are at least 2 of the same installed so: 2x 4 gb and 2x 8gb should work fine. For more info, this link

  • Link is broken. Commented Nov 15, 2017 at 18:12
  • Link has been updated!
    – Jules
    Commented Jan 11, 2018 at 10:06
  • What do you mean "at least 2 of the same installed"? If a computer has 2x4gb, could you add a single 8gb ram stick? (Totalling 16gb)
    – Solvitieg
    Commented Jul 22, 2020 at 20:46
  • No, it can’t be a single module, the total ampunt of modules installed needs to be a multiple of 2.
    – Jules
    Commented Jul 23, 2020 at 21:59

I have mixed sizes on a 2012 iMac with no problems that I am aware of. I recently purchased the iMac 18,3 5k 27-inch 2017 model. I will be purchasing 32.0GB (2x 16GB) 2400MHz DDR4 to go along with the 8GB (2x4GB) 2400 MHz DDR4 that comes pre-installed from Apple. In 2012, Apple told me there was no problem mixing sizes then, the same rules apply to the new models.

Be sure to match the other specs of your old and new RAM (MHz and DDR4 type), but unlike in other things in life, "size doesn't matter"

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