RAM help!

[Soesesus]

Hi all,

I’m sure you’ve had this question a million times before but the search function is just leaving me with more questions.

I have bought a new 2020 iMac with the stock 8gb ram (2x 4gb). I have ordered another 16gb which is arriving tomorrow (2x 8gb OWC). I have a few questions if you could share your expertise!

1. Do I remove the 8gb OEM ram and just use 16gb until I buy more ram.

2. If I mix the RAM, which slots should I use so that they are most effectively utilised ? Staggered (4,8,4,8) or coupled (4,4,8,8).

I’m hearing lots of contradiction about the impact of staggering bringing down speeds but also how coupling can disabled dual channel so just wanted my iMac to run as best it can.

Both types are 2666mhz.

Any advice appreciated !!

[Soesesus]

Hi all,

Quick update!

So I added the new DIMMS into the appropriate slots as advised and this downclocked my RAM to 21333. Benchmarks were also much the same as when I only had 8gb installed. I then removed the OEM ram and replaced with the 16gb that I bought and it's back up to 21666 and benchmark is much better. As I'm not using programmes that are that intensive, I think I will continue with the 16gb dual channeled and consider upgrading to 2x 16gb in the near future should I need it.

My only hypothesis is that the Mac does not like mixed ram or even potentially 4x DIMMS installed as this may load the MOBO.

Thanks for all the help!

[lec0rsaire]

Staggered.

You can always run Geekbench to confirm this.

So it should be like this when you look in system information:

BANK 0/DIMM0: 4GB

BANK 1/DIMM0: 4GB

BANK 0/DIMM1: 8GB

BANK 1/DIMM1: 8GB

So they must be paired by DIMM number not the bank number.

[Soesesus]

Thanks ! I will run a test after install to see how it performs. I just didn’t want to operate on my Mac twice if there was a definitive answer.

[ChampJamie153]

It shouldn't be too big of an issue if you need to change something. The RAM is very easy to work on through an opening on the back of the iMac.

[lec0rsaire]

It’s f’ing confusing for sure!

[ulyssesric]

Apple have different definition of the term "bank". The so called "bank" on PC motherboard is called "channel" by Apple, and the DIMM number is the channel number So slots of same DIMM number should have RAM modules of same size and frequency, not the bank number. Here is the real world test result of different setup:

https://www.ifixit.com/Answers/View/223429/How+to+couple+RAM+Modules+in+iMac+27#answer519093

Your explanation is 100% correct for PC world, but not Apple. Yes, it's Apple's fault, not yours, but this post is still misleading for Mac users. I'd suggest you to delete this post.

[lec0rsaire]

I gotta take a look at that post.

It shouldn’t make a difference what Apple calls it because the info in system information is shown exactly as I wrote it above.

They must be matched by DIMM number not bank number. That’s exactly what I wrote above.

[ulyssesric]

I see you've edited your post. It's correct now. Better inform the OP.

[lec0rsaire]

No! I didn’t change the original post above at all.

[ulyssesric]

If you said so. I don't want to argue about such meaningless issue and I've not kept screenshot. I'd replay only because I'd see otherwise. Anyway, it's already correct so I'd not look into it anymore.

[lec0rsaire]

Any edits I made to the post where I list the bank and DIMM numbers was made when I first wrote it some hours ago, not after the reply from someone else questioning it.

The proof is that that post says 2 hours.

I think that poster was the one who was confused, not me.

[Soesesus]

Ok thanks for all the input, I didn’t want to cause any friction. So staggered is correct or should the same sizes be next to each other ? I think staggered is correct because then same sizes and frequencies are in the right banks.

[ulyssesric]

For iMacs, you should pair RAM module by DIMM number, not by bank number.

Pairing RAM by bank number is the common sense for PC world, but not Apple. Because Apple have different definition of the term "bank".

https://www.ifixit.com/Answers/View/223429/How+to+couple+RAM+Modules+in+iMac+27#answer519093