I'm about to upgrade the memory on my 2019 27" iMac. I have a choice between:
(a) buying 2x32GB and installing them alongside the existing 2x8GB;
(b) buying 4x16GB and removing the existing 2x8GB.
Does it make any difference in performance if the modules are two different sizes versus all the same size? (so long as they're installed pair-wise in the proper banks, of course)
iMac Line (2012 and Later)
As long as they are properly paired in the slots, it won't
matter.
Also, buy only quality RAM from either:
or Crucial
BTW, use the Crucial selection tool to insure you get the proper RAM.
Generic bargain basement PC RAMs will be a source of all manner
of unexplainable problems.
As long as they are properly paired in the slots, it won't
matter.
Also, buy only quality RAM from either:
or Crucial
BTW, use the Crucial selection tool to insure you get the proper RAM.
Generic bargain basement PC RAMs will be a source of all manner
of unexplainable problems.
put them in the two empty slots and leave the original two DIMMs alone.
Correct - in iMacs with a vertical slot setup, they are now paired in slots 1 + 3 and 2 + 4. They used to have to be "paired"; it is no longer a necessity, but, in my personal opinion, it doesn't hurt to do so.
And, I will go against the trend here: I'd go with 4 x 16 GB. As well, you won't be dealing with "surplus memory" - the way it is now working is: whatever amount of RAM you have, it will all get used. The new slogan is: Unused RAM = wasted RAM.
I would get 2x32GB now, install them in place of the original 2X8GB and return them for a small rebate from OWC.
https://eshop.macsales.com/item/OWC/2666DDR4S64P/
Rebate info:
https://eshop.macsales.com/tech_center/support/rebates/
Check prices periodically for when they drop and get the other 2X32GB in a couple of years, if you ever think you need more and want to max out the machine. As faster computers and RAM are released in the future, the older RAM tends to drop in price. So, the stock RAM you have will be worth less as a rebate or for re-sale in the future as well.
RE: original 2X4GB??? Well, adding more will definitely improve the performance of your machine. That bare-minimum offering of RAM in a base model is really not enough, even by a few years ago standards. Go ahead and return it for the $10 rebate, having that extra 8GB will probably make very little difference once you have the 64GB RAM in there.
Official Apple iMac memory details: Install memory in an iMac - Apple Support
Officially, this iMac doesn’t support 32 GB SDRAM. Per various listings, a 128 GB (4 x 32 GB) configuration should work.
Interestingly, Apple does not mention memory pairing, nor DIMM banks, nor interleaving, either.
Based on a note else-network, the SDRAM DIMM interleaving pairs on an iMac 2019 are the odd and the even banks; that’s the DIMM 0 slots, and the other pair is the DIMM 1 slots. (Apple slot-labeling terminology here tends to be... unique.)
It should make no difference as long as they are the correct specs.
OK, I'll go ahead and buy 2x32GB. A bit more expensive than 4x16GB, but I end up with more memory because I keep the original 2x4GB. (not 2x8GB... that was a brain fade on my part.) And I don't have to deal with surplus memory.
The installation video on OWC (macsales.com) shows removing the original two DIMMs from the first (top) and third slots (presumably banks 0 and 2) before installing four new DIMMs, filling all the slots. So if I add 2x32GB the obvious thing to do is to put them in the two empty slots and leave the original two DIMMs alone.
27" iMac - 4x16GB versus 2x8GB + 2x32GB?
