Can I add different size RAMs to iMac 5K? 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.



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?

Thanks
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