Upgrading RAM on a new iMac

[strangeasangels66]

Sorry if this is a silly questions but I got a new iMac with 128 capacity ram. If I want to upgrade the stock ram which currently has 8 (4/4). I will eventually upgrade to 128 but for the time being I bought only a pair of 32 GB sticks (Crucial brand). A couple of questions:

1) Can I add the new ram to the empty slots or is it bad to mix?
2) If not, do I simply replace the old RAM slots with the new?

I am probably over thinking this but would appreciate your input. Thanks.

 

[Sheepish-Lord]

Best practice is to use matching ram and all the slots

 

[strangeasangels66]

But Apple isn't using all the slots. They only have 2 occupied with 4 gigs each. The other two are empty.

 

[pmiles]

Install memory in an iMac - Apple Support

Get memory specifications and learn how to install memory in iMac computers.

support.apple.com

Unfortunately, not all RAM plays well together, hence the suggestion by Sheepish-Lord to basically use the same RAM in all the slots. While mixing RAM is doable, finding the right mixture is often a trial an error situation... making just replacing the existing RAM with new RAM often the more headache free option.

 

[theluggage]

1) Can I add the new ram to the empty slots or is it bad to mix?

Yes - that should work if they are the same specification of RAM (PC4-21333 or whatever). If you bought the recommended RAM from Crucial then odds are it's exactly the same brand of Micron sticks that Apple uses.

The wrinkle is that, for maximum performance and to avoid problems, sticks should be installed in matched pairs of the same size, type and brand, so that each of the two channels has a matching sequence of sticks. On the 5k iMac, this translates to an alternating pattern like:

Slot 1: 4k
Slot 2: 32k
Slot 3: 4k
Slot 4: 32k

...and the original 4k sticks should have been installed by Apple in slots 1 and 3, so just fill in the empty slots.

Obviously, if you get problems, just get rid of the old RAM and have the 32GB sticks in slots 1 and 3.

Disclaimer: this was true as of my 2017 5k iMac - at which point this was thoroughly thrashed out in threads like this. I'm not aware of it having changed in later 5k iMacs.

 

[BrianBaughn]

Be aware that mismatched RAM issues may not appear immediately and the warranty won't cover RAM that's not working properly just because it's mismatched with existing RAM.

 

[curnalpanic]

Sounds like all RAM sticks must be manufactured together in the same factory during a full moon on the equinox, to be on the safe side.

 

[Fishrrman]

OP:

If the new RAM works on "the first try", just use it.

If it DOESN'T work, you might try re-arranging the DIMMs in the slots. Several re-arrangements are possible. Try them all.

If that STILL doesn't work, my suggestion is that you "set the factory RAM aside in a safe place" and use the 2 32gb DIMMs (for a total of 64), and "be happy" that way...

 

[rpmurray]

Sounds like all RAM sticks must be manufactured together in the same factory during a full moon on the equinox, to be on the safe side.

You forgot the sacrificing of a virgin.

 

[wilberforce]

Sorry if this is a silly questions but I got a new iMac with 128 capacity ram. If I want to upgrade the stock ram which currently has 8 (4/4). I will eventually upgrade to 128 but for the time being I bought only a pair of 32 GB sticks (Crucial brand). A couple of questions:

1) Can I add the new ram to the empty slots or is it bad to mix?
2) If not, do I simply replace the old RAM slots with the new?

I am probably over thinking this but would appreciate your input. Thanks.

What exactly is your "new iMac"?
If it is a 2020 27" iMac it has some quirks about RAM: all sticks must be the same size and identical (with some exceptions) else RAM performance drops. Still works, but at a slower speed. Best not to mix.
Other model years are not as fussy.

 

[Eugen Mezei]

What exactly is your "new iMac"?
If it is a 2020 27" iMac it has some quirks about RAM: all sticks must be the same size and identical (with some exceptions) else RAM performance drops. Still works, but at a slower speed. Best not to mix.
Other model years are not as fussy.

What is the source or explanation for that statement?
Are the two channels not independent so that you have to pair only two per channel? (Meaning only two and two modules have to be identical, but not all 4.)

 

[wilberforce]

What is the source or explanation for that statement?
Are the two channels not independent so that you have to pair only two per channel? (Meaning only two and two modules have to be identical, but not all 4.)

There are some long threads on upgrading RAM in the 2020 iMac, but this is what Apple says - note the red circled words appear only for the 2020 iMac, and not for any other models. Why, who knows. It may just be a firmware bug. Regardless, if you mix DIMM sizes across 4 slots in the 2020 iMac, either the speed drops from 2666 to 2133 MHz, or you lose full dual channel (depending on how you mix them), and the result is that the tested RAM transfer speed drops, for example as tested using NovaBench.

 

[WarthogARJ]

Sorry if this is a silly questions but I got a new iMac with 128 capacity ram. If I want to upgrade the stock ram which currently has 8 (4/4). I will eventually upgrade to 128 but for the time being I bought only a pair of 32 GB sticks (Crucial brand). A couple of questions:

1) Can I add the new ram to the empty slots or is it bad to mix?
2) If not, do I simply replace the old RAM slots with the new?

I am probably over thinking this but would appreciate your input. Thanks.

Hi,
It's a used iMac, but new to you: correct?
In any case, it cost > $1,500 I'm sure.
Maybe > $2,000

Am assuming you have some uses that need 128GB RAM: which is a HUGE amount for 99.9% of Earthly inhabitants...:-}

Bottom line is if you doing anything that is RAM constrained, then OPTIMISING the RAM you have is important.
If YES, then do NOT use the 2 x 4GB.
Rather instead of buying 2 x 32GB, do as follows:
(1) If short of money, and cannot get girlfriend/boyfriend/wife/husband/moth/sister etc to go on CraigsList for SugarBay's 'r Us, then buy 4 x 16GB
And when Craigslist comes thru, sell the 4 x 16GB, and buy 4 x 32GB
(2) If not short of $$$ (or if you already know about CraigsList), do it right, and but 4 x 32GB

In any case, benchmark how it runs with the supplied RAM.
With a benchmark that correlates with your work.
And surely if you do work with something that can actually USE 128GB, then it will be easy to find the right benchmark(s).

Then benchmark with whatever CraigsList efforts will be able to buy you.
And indeed, benchmark what you get if you DO run a non-matched set of RAM.

Summary: if you are doing something that is truly RAM constrained then running a set of un-balanced RAM is a bad idea.

Alan