iMac 2020 - Downgrade OS

[blufrog]

Hi,

My father has what I think is a 2020 Intel iMac 4K, and it is currently running Monterey, but it is very very slow.

I have checked to see what is running on it, and deleted a lot of rubbish that started up at boot, but this did little to improve things.

I read that Monterey was the first OS to be "optimized for Apple Silicon" which I assume was the M1. Is this why it is slow?

I can't remember which OS it originally shipped with, but I was thinking of rolling it back a version to 11.x and seeing if it improved things.

Is there a recommended way to do this? I know I should be able to reset it back to the OS it shipped with, but nothing from that era works from an online perspective. A massive problem is the app store no longer works, so nothing can be re-installed from it.

Any help/advice appreciated.

 

[Bigwaff]

Does the iMac have a Fusion Drive? If so, that is most likely the culprit. Fusion Drives prone to failure. Slow performance harbinger of death. Replace with SSD.

 

[Ruggy]

Fusion drive is likely the answer but when you say slow is it slow at everything? Is it slow trying to load web pages, is it slow when you are handling big files or just everything is slow?
If the problem is outdated apps then you could try going to Sequoia but it maybe that the HD is nearly full too so check storage and that will slow things down. Cleaning up start up items can help but you've done that. If you've got Google or some such starting that can slow things down as they have a time out if you block ads.
It's not really that old and we've got 2020 machines here still running fine and one 2016 still zipping along.
There's a lot more to check
Having an SSD is probably the answer though.
If you aren't an Apple person the Apple logo top left will lead you to checking on system settings, resources, storage etc and it may well be worth running hardware diagnostics to see if the drive is failing (you do that from start up but it changes with the OS I think so you'll have to look that up).
You may have malware too so you could try Malwarebytes free version to check for that

 

[curnalpanic]

Yeah, use an SSD and maybe a fresh install of the latest supported that is not Tahoe.

 

[Fishrrman]

I tried searching everymac.com for a 2020 4k iMac, and came up with ... nothing.
2019 4k iMac, yes, but 2020? No.

These look like they came with "fusion" drives. A fusion drive is actually TWO drives "melded" into one volume:
- small SSD (about 32gb)
- larger HDD (1tb)
They worked ok when new, but can get "clogged up" as they get older.

The advice given above about moving to an SSD is good...
BUT
... you almost certainly DO NOT want to try to open the old iMac, as the job isn't going to be easy. Quite difficult on these, I understand.

There's "a better way" to speed things up.
That is:
1. get an EXTERNAL SSD, 1tb in size (or larger if you want). It should be "USB3.1 gen2", and should yield 10gb speeds (older, plain-vanilla "USB3" drives are generally 5gb).
2. Connect it to the iMac USBc port (don't use USBa) and format it to APFS, GUID partition format
3. At this point, you need to decide to either:
3a. Start with a fresh OS install, or
3b. "Clone over" the contents of the internal drive to the new SSD.
Cloning is the "fast n easy" way to go, and it just may work and solve your problems. I'd suggest you try that first.
Here's how to proceed:
a. Download the app "SuperDuper" by clicking this link:

https://shirt-pocket.com/mint/pepper/orderedlist/downloads/download.php?file=https%3A//shirt-pocket.com/downloads/SuperDuper%21.dmg

SuperDuper is one of the easiest-to-use apps out there. No instructions needed, really. You'll see what to do. It's also FREE to use for what we're going to do.
b. Use SD to clone the contents of the iMac internal drive to the SSD.
c. When the cloned backup is done, open the Startup Disk settings pane
d. Do you now see the external SSD there, as well as the internal drive? Then you know the clone "is good".
e. Set the SSD to be the boot drive (password required).
f. Reboot
g. You should now boot from the SSD. If it's "a good boot", have your father log in and "look around".
Do things look ok?
That's really all there is to it.
You can just "leave the internal fusion drive as it is". It won't hurt anything.

By the way...
everymac.com shows the factory-installed OS for a 2019 4k iMac to be 10.14.4 "Mojave".

I still use Mojave on my 2018 Mini -- it's an excellent OS version, and the last that can run older 32 bit apps.

But once you're booting and running from an SSD (even external), things will probably go considerably faster, even with the Monterey OS.

The alternative...
Since the iMac is now 7 years old, you might start thinking about a replacement in the future.
I'd suggest (rather than iMac), a Mac Mini.
But be aware that supply on the m4 Minis is VERY constrained right now.
Better to wait for the m5 Mini that's probably coming in the fall...

 

[Ben J.]

b. Use SD to clone the contents of the iMac internal drive to the SSD.
c. When the cloned backup is done, open the Startup Disk settings pane
d. Do you now see the external SSD there, as well as the internal drive? Then you know the clone "is good".
e. Set the SSD to be the boot drive (password required).
f. Reboot
g. You should now boot from the SSD. If it's "a good boot", have your father log in and "look around".

No cloning software will be able to clone a drive to create a bootable Monterey volume. Since Big Sur and Monterey, the mac has a signed system volume, which means a bootable volume can only be created with a macOS installer.

My advice would be to get an external SSD, install a modern macOS version of your choice on it, boot from it, and in the first run, when the Migration Assistant asks if you want to import a user account, simply point it to the one on the internal drive. Then set the mac to boot from the external SSD in system preferences.

The 2020 imac should be able to run any version up to and including Tahoe.

Added: @OP: If you think you'll be ok with the very small drive size like 250GB something like this will be a good deal with very good performance (10gbps). Or a 500GB like this.

 

[blufrog]

Hi,

AFAIK it has an SSD only, not Fusion.

It's an iMac Retina 4K model 16,2 "Late 2015" - quite a bit older than I thought!

It's running Monterey (12.7.6) and AFAIK this is the last version it supports.

Yes, the whole thing is equally slow.

It has a 256 GB SSD (not Fusion). There is 55 GB free on the disk.

 

[chrfr]

I think the computer probably just feels slow because it's old and slow. Downgrading the OS won't have an appreciable difference in performance. Just because the OS will also run on Apple Silicon doesn't mean it got much worse than an earlier version.

 

[ResolutionNZ]

This is the repair guide for the model you mentioned later on in the thread. It doesn't look like something most people would want to try. Running the OS off an external drive seems to be a better option.

Or you could replace it with a newer iMac and not worry about the growing number of software compatibility issues you'll start running into on a Monterrey device now that intel Macs are no longer being supported into the future. The screen has the same display size, so you won't be losing out on anything there.

The current iMacs still support Sequoia if you want to avoid Tahoe. Next gen models will likely start running on Golden Gate. Just to clarify, the first MacOS to support M-series chips was Big Sur back in 2020.

 

[benholt]

That machine — Late 2015 4K — has a SATA SSD (capped around 500 MB/s), and the killer on it under Monterey isn't really the OS version, it's mdworker plus the rewritten Metal window server hammering the SATA bus in the background. On my kid's 2015 MacBook Air (same-era logic), running sudo mdutil -i off -a from Terminal to disable Spotlight indexing on the boot volume was the single biggest win — Finder and boot time went from painful to workable.

If that doesn't clear enough of it, dropping to Big Sur helps a little but not dramatically. The version that actually feels right on Broadwell is Mojave, but you'll lose modern browser compatibility quickly. Realistic bet on a machine that age: keep Monterey, kill Spotlight, uninstall Chrome/Firefox and stick to Safari, and accept it's near end of usable life.

 

[Fishrrman]

At 11 years old, it may be time to start thinking, "replacement".

DON'T buy another iMac, however.

Wait until the m5 Mini is released (probably Oct), and get one of those.
But don't "cheap out" on it.
Get 24gb or 32gb of RAM, and at least a 512gb SSD (1tb is better).

Pick up either a 27" 4k or 5k display.

I wouldn't put much (any?) money into an 11-year-old iMac now.
Just try to keep it going until a good replacement arrives...

 

[blufrog]

That machine — Late 2015 4K — has a SATA SSD (capped around 500 MB/s), and the killer on it under Monterey isn't really the OS version, it's mdworker plus the rewritten Metal window server hammering the SATA bus in the background. On my kid's 2015 MacBook Air (same-era logic), running sudo mdutil -i off -a from Terminal to disable Spotlight indexing on the boot volume was the single biggest win — Finder and boot time went from painful to workable.

If that doesn't clear enough of it, dropping to Big Sur helps a little but not dramatically. The version that actually feels right on Broadwell is Mojave, but you'll lose modern browser compatibility quickly. Realistic bet on a machine that age: keep Monterey, kill Spotlight, uninstall Chrome/Firefox and stick to Safari, and accept it's near end of usable life.

Oh...interesting. I remember when he first got it, how snappy it was. I still have my iMac 5K (running El Capitan) and it seems faster than his now, so something changed, but no idea what or when.

He was talking about getting a Mini (I have one and he likes it) so that will likely be his next machine when the M5 is released.

A shame these systems are obsoleted by the OS. I have the same issue with my 5K and MBP. Hardware is fine, but nothing works (app store), completely stopping me installing anything. XCode is my biggest problem (no updates = no bueno).

Neither of us are limited by them being Intel Macs, so legacy support isn't a deal-breaker.