iMac RAM and slots

I've just upgraded the RAM in this 2020 iMac from the base 8GB (2 x 4GB in slots 2 & 4) to 1 x 32GB in slot 1. Not sure if that's the best way but it's working so it can't be completely wrong!

(I bought it that way because 1 x 32GB was a hell of a lot cheaper than 2 x 16GB)

It seems a shame to have 8GB sitting around doing damn all, but I can't find out if it's OK to have an odd number of modules installed, ie put the 4GB modules back into slots 2 and 4 to give me 40GB. I don't really need it, but it would be nice to have

Even if it works I gather there'll be a performance hit due to the disparity in the sizes, anyone got any advice?

Geekbench5 scores before and after the additional modules are installed - presuming the computer doesn't say 'no' 😂 once you pop them in.

In reply to a post by Pheasant:

presuming the computer doesn't say 'no' 😂 once you pop them in.

Ta for the Geekbench suggestion, I'll think about that but I'm not over-concerned about performance loss unless it's likely to be substantial. It's a matter of whether it's likely to work! (And I'd like to learn a bit more about how Macs handle the slots and channels if someone can explain it in Class 101 terms.)

I only bumped up the RAM because, especially with multiple HD streams, Chrome was hitting the swap file far too much for my liking with only 8GB- no real problem with an HDD, but not so nice with an SSD

So far it seems OK, not coming within 8-10GB of needing to swap anything out. And it all feels much "snappier", presumably from not needing to bother so much with fancy memory management. It's noticeable that the compressed memory is zero, it never was before!

The old saw is true- you can't have too much RAM


edit- typo

Edited by billford (Fri 11-Feb-22 17:15:25)

You've already taken a performance hit by opting for single-channel RAM. Mixing aftermarket RAM with the Apple original is not recommended but if you need the extra at the expense of performance then go for it.

I'd buy another 32GB module.

In reply to a post by TinyMongomery:

You've already taken a performance hit by opting for single-channel RAM.

Ah, I wasn't aware that would be the case, thanks. As my reply to Pheasant indicated, my knowledge of how Macs handle RAM modules is minimal... So if I put the two old modules back, would I be mixing single and two-channel RAM? Even if that would work, it doesn't sound good.

In reply to a post by TinyMongomery:

Mixing aftermarket RAM with the Apple original is not recommended but if you need the extra at the expense of performance then go for it.

I'd buy another 32GB module.

I don't really want two performance hits... and tbh it doesn't look as though I'll really need any more memory, but the thought of another 32GB had crossed my mind (I'm getting it from Crucial not Apple so I wouldn't need to take out a mortgage!)

3 modules should work; performance will depend on the specs of the individual modules. Being pragmatic, it does no harm to try it and see what before and after tests reveal. TBH, I've never found the need for more than 32GB with a couple of VMs running. I find storage speed to be more important than RAM nowadays, and that's good enough on any Mac from the past few years. You even get better performance from an external SSD than with the internal HDs of yesteryear.

In reply to a post by TinyMongomery:

You've already taken a performance hit by opting for single-channel RAM. Mixing aftermarket RAM with the Apple original is not recommended but if you need the extra at the expense of performance then go for it.

I'd buy another 32GB module.

I thought that, but was not sure if MAcs suffer from that problem, but since the Imac is from 2020, it would be Intel based, I presume so being intel based it would still suffer from single channel memory.

Just googled it and found this support article from Apple…

https://support.apple.com/en-gb/guide/imac/apdd768f6...

Interestingly it’s only when you select the 2021 version of the iMac with Monterey 12 that you get the additional caveat at the end, I’ve highlighted in bold. The earlier 2019 and 2020 versions running Catalina and/or Big Sur don’t have the caveat:

“You can install additional memory in the free slots or replace the memory in the filled slots with 4 GB, 8 GB, 16 GB, or 32 GB memory modules, for up to 128 GB of memory. For best performance, use memory modules with close capacities. For example, you’ll get better performance using two 8 GB and two 16 GB modules compared to two 8 GB and two 32 GB modules.”

In reply to a post by Pheasant:

Just googled it and found this support article from Apple…

https://support.apple.com/en-gb/guide/imac/apdd768f6...

Interestingly it’s only when you select the 2021 version of the iMac with Monterey 12 that you get the additional caveat at the end, I’ve highlighted in bold. The earlier 2019 and 2020 versions running Catalina and/or Big Sur don’t have the caveat:

“You can install additional memory in the free slots or replace the memory in the filled slots with 4 GB, 8 GB, 16 GB, or 32 GB memory modules, for up to 128 GB of memory. For best performance, use memory modules with close capacities. For example, you’ll get better performance using two 8 GB and two 16 GB modules compared to two 8 GB and two 32 GB modules.”

you’ll get better performance using two 8 GB and two 16 GB modules compared to two 8 GB and two 32 GB modules.”

umm, I did not know that, I wonder if that is just a Mac thing, I have two 8GB and two 16Gb sticks in this machine.

I have no idea why it is different for Monterey, MAc Os went 64bit before that .

I put a new hard drive in an older imac a few years ago, what a pain in the neck, apart from taking the thing apart, because we changed the hard drive, the fans wanted to go full blast, thankfully, there is some software called ssd fan something or other that keeps it under control. Not the best way, but the machine works ok and is still working, but is used for office work these days.

This is the problem with Apple machines as time gone on, more difficult to update, so why am i thiking of going for a Mac mini?

Speaking of fans…I’ve tried to get the fans running in my M1 Max based MacBook Pro but they stubbornly refuse to go above 0 rpm. Maybe there are no fans in there!! Really need to find something to proper light up all 42 cores, the various media and neural engines and all the RAM. Perhaps they’ll budge then 😂

As you say, for better or worse now they have effectively become non-upgradeable. With Apple Silicon, RAM is part of the SoC. You have to forward spec. for the life of the machine.