Question on Module Order

27" 2013 iMac came with 8GB ram (2x4GB) and the modules were in every other slot.
I added 16GB (2x8GB) into the other slots and received 3 beeps. I then changed them such the 2 4G modules were together and the 2 8G modules were together.

Here's the rub: Concerned with having them out of order because the 4G modules are single ranked and the 8G modules are dual ranked (it treats an 8 as if it where 2 4G sticks)

Does the actual order of memory matter when mixing on the new iMac (may not have had the memory seated properly the first time.) I know you can have addressing and performance issues on some platforms if they are not matched. It seems to be working fine but I don't want to lose my Mega-hertz..

Thanks for your time and glad to be a new member here.

27" 2013 iMac came with 8GB ram (2x4GB) and the modules were in every other slot.

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Are you sure of that? I have the same machine (27" iMac, late 2013 model) and the 2 x 4 GB modules are in the upper first two slots. The bottom two slots are empty. Or perhaps I'm misunderstanding what you mean by "every other slot"?

Does the actual order of memory matter when mixing on the new iMac (may not have had the memory seated properly the first time.) I know you can have addressing and performance issues on some platforms if they are not matched. It seems to be working fine but I don't want to lose my Mega-hertz..

Click to expand...

The modules should have been seated properly and placed in the correct slots when the machine left the factory (unless you moved them). In any event, the larger modules should be placed in the first two banks (upper slots) and the smaller modules in the lower bank. However, it won't matter if those are reversed.

What you don't want is to put different modules (different size) mixed in the same bank. And always use the correct modules for your model iMac. Your machine uses:

Memory Slots 4 - 204-pin PC3-12800 (1600 MHz) DDR3 SO-DIMM

And welcome to the Mac Forums!