Very slow and laggy iMac

Question

abhay28 Author

Level 1

12 points

Very slow and laggy iMac

Hi,

I have an iMac (21.5-inch, Late 2015)

Processor : 2.8 GHz Quad-Core Intel Core i5

Ram: 8 GB 1867 MHz DDR3

All seems ok but the iMac is very slow. I have even wiped out the hard disk and reinstalled BigSur but still no improvement in response.

By slow I mean if I click to start any application like mail, the rainbow circle will be there for around 45 seconds before the app will open. Some other apps like Safari takes 2 min to be usable.

Any search in mail will result in unto 5 min wait time.

Please note this is freshly installed ( not rerintall) copy of BigSur. Disk Utility (First Aid) shows no error.

Have a Magic keyboard, however, if I press "D" while starting, it does nothing. Maybe cannot use bluetooth at that stage.

Connected an old HP wired keyboard and when I press "D" on startup, it takes me to Internet recovery.

Hence, cannot run any diagnostics.

I'm in Sydney ( under lockdown) so cannot even take it to Apple store.

Any other advise you guys might have?

iMac 21.5″, macOS 10.13

Posted on Sep 9, 2021 7:03 PM

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Answer 1

Jack-19

Level 8

46,188 points

Sep 9, 2021 7:21 PM in response to abhay28

Welcome to the Apple Support Communities.

I believe we need to proceed with an EtreCheck report. EtreCheck is a useful App to diagnose and identify issues, both hardware and software. It is trusted by many users. Please follow the steps outlined below:

Navigate to: https://etrecheck.com and get the free version of EtreCheckPro.
Download it. It is a free and trusted app. It is often recommended here on Apple Support Communities.
Open EtreCheck, and before running the report, be sure to check “Allow full Drive Access” at the bottom of the EtreCheckPro window.
Run the report, and put it in a post, as seen here: https://discussions.apple.com/docs/DOC-250000211. We will then examine the report for issues in your Mac.

Jack

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Answer 2

Jack-19

Level 8

46,188 points

Sep 9, 2021 8:02 PM in response to abhay28

The reason your iMac is very slow is due to the 5400 rpm hard drive. Very slow. If you use an external SSD and run macOS from that, it will make your Mac 10 to 30 times faster for storage. For more info, instructions, and what external SSD to buy, please read: How to Setup and Use an External SSD as y… - Apple Community.

Jack

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Answer 3

abhay28 Author

Level 1

12 points

Sep 20, 2021 3:10 AM in response to Jack-19

Hi Jack,

I ended up buying a Crucial MX SSD and a SSD Case to connect it to iMac with USB-A cable. After installing BigSur on external SSD, my Mac feels like flying. Gone is the super sluggish experience. Seems my Mac in new again.

Big thanks

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Answer 4

abhay28 Author

Level 1

12 points

Sep 11, 2021 3:31 PM in response to Jack-19

Thanks Jack.

I've bought a SSD hard disk from Samsung(MU-PC500T) . However, due to lockdown have to wait a few days until it is delivered.

In the meantime I'm mostly using Linux on this machine as Linux is not facing any slowness that OSX is exhibiting. To be true, linux just flies. I can open multiple programs and shuffle between them, no issues. Garuda Linux is very resource hungry as compared to some bare bones like Arch or Fedora, yet Garuda Linux is at least 10 times faster than OSX on this very hardware. I always thought that OSX ( BigSur) is super optimised for iMac and should be best performing but Linux has broken the myth.

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