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A friend has a 21" i3 iMac 2019 with 8Gb RAM and it's horrendously slow. He's had Apple Support and Geniuses look at it and they cannot find a problem. The only extra software he has is Photoshop elements and simply loading Photos or Safari takes several minutes.

I've taken it home and wiped the hard drive and did a clean install of Sonoma and it's better but not great - my 2010 27" i7 iMac (albeit with 20Gb RAM) and M2 MacBook Pro both run rings around it operating instantly. This isn't just "Slow compared to more powerful machine" but slow as in "What am I waiting for?"

My wife's old 11" Macbook Air with 4Gb was faster - is the slowness just a consequence of the new OS with what could be considered a low amount of RAM (8Gb) or is there anything else that could cause this slowdown?

There is nothing untoward in Activity Monitor.

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  • What year is your iMac? Does it have an HDD or an SDD?
    – lhf
    Commented Jul 9 at 11:29
  • 2019 I think and not sure (it's at home and not mine), but judging by Apple's tech specs page it's either a 256Gb SSD or a 1TB fusion drive. which could be the issue. discussions.apple.com/thread/252753807?sortBy=best
    – Steve Ives
    Commented Jul 9 at 11:52
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    Worth saying that "wiping the disk and reinstalling the OS" is not necessary on Macs with Catalina or later. At most, you just need to do "erase all content" from System Settings. I'd agree the cause is probably the mechanical hard drive.
    – benwiggy
    Commented Jul 9 at 13:35
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    Wild guess: The CPU cooling could also be a factor. The cooling paste between CPU and heat spreader can become dry and loose its function, the CPU would have to throttle down due to very poor cooling. Removing the cooler, cleaning the CPU, and applying new paste may help.
    – DarkDust
    Commented Jul 10 at 8:04
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    When you say "there is nothing untoward in Activity Monitor" are you (1) looking at the CPU column with (2) "All Processes" instead of "My Processes" selected in the View menu and (3) sorting by descending %CPU, monitoring for any spikes in usage during periods of slowness? Additionally, how much swap is in use (in the bottom of the Memory tab) when your machine is being slow?
    – pion
    Commented Jul 10 at 9:24

1 Answer 1

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From this article : https://discussions.apple.com/thread/252753807?sortBy=best is looks as though this machine might have the 1Tb fusion drive and it's the HDD part of the setup causing the issue.

I have a fast USB-C SSD so I will install MacOS on that and set it up as the boot drive to see if that resolves the issue.

Edit : It did. The difference is amazing. I've had 'slow' machines that have benefitted from an SSD but I've never seen one so completely hamstrung by having the OS on an HDD (and one with 32Gb of SSD to accelerate it).

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    If that fixes the speed, consider an internal drive replacement with a more-modern SSD rather than the combo drive. That drive would do well in an external USB enclosure where its really just holding data.
    – Criggie
    Commented Jul 9 at 23:54
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    Yep - it was the internal drive (a 1Tb fusion drive consisting of a 1Tb HDD and a 32Gb SSD). I've never seen a computer react this badly to a relatively slow hard drive - starting Photos or Safari or Mail was taking over 30s. Now, with an external M2 1Tb SSD it's instantly responsive. I'm guessing that the new OSes are so optimised for SSDs that it's tripping over itself with I/O tasks and so rather than taking 3,4 5 etc. times' longer its taking 50-100x longer. It was better after the wipe and reinstall, but still unacceptable.
    – Steve Ives
    Commented Jul 10 at 9:12
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    @Criggie - I think upgrading the internal drive is a lot of work on these machines. I'd also like to chuck in another 8Gb but I think that's a non-starter too. My friend (who is completely non-technical) will be happy with the new performance (he was just going to trade it at Apple for a MacBook) and won't care about the black box velcroed to the rear :-)
    – Steve Ives
    Commented Jul 10 at 9:15
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    @SteveIves It could be that the hard drive is simply failing rather than not being fast enough: when the data can't be read properly, HDD retries again several times, causing everything to wait for the retries to finish. I had this happening on my old MacBook after every long trip, forcing me to buy new HDD every year.
    – Dmitri Urbanowicz
    Commented Jul 10 at 10:42
  • @SteveIves yeah - from memory imac drive upgrades require levering off the face-glass without chipping or breaking it - fun times.
    – Criggie
    Commented Jul 10 at 13:00

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