I have this:

  • iMac (21.5-inch, Late 2012)
  • 2,7 GHz Intel Core i5
  • 16 GB 1600 MHz DDR3
  • NVIDIA GeForce GT 640M 512 MB

Some days ago I updated to Sierra 10.12.6, and all my apps. My HD currently have about 350 GB free space.

Still, it runs quite slow after upgrading from El Capitan to Sierra.

Any of you had the same issue? How to solve?


3 Answers 3


Putting an SSD inside will give the most speed boost possible for general computing. If you have a specific benchmark or measurement you want to optimize, there might be other options.

Since that’s an internal upgrade, you should consider what value you can recoup selling it used and buy a better / newer used Mac than trying to upgrade internal parts on most iMac.

Since you have a hard drive, you will get the best performance with a hundred free GB and rebooting once a week or so. Other than that, watching for RAM hogs and keeping browser tabs under control are good tips as well.

  • I don't know if it would be possibile to upgrade to ssd, honestly.. Sep 12, 2017 at 14:49
  • I wouldn’t, personally but I’m comfortable selling and buying used so it’s less of an only option for me. I’ll add HDD tips.
    – bmike
    Sep 12, 2017 at 15:53
  • SSD should be possible. Check out OWC SSD Upgrade Kits.
    – railsdog
    Sep 12, 2017 at 17:11
  • @Stratboy - you can upgrade an iMac HDD. The toughest part is cutting the glue around the display. Once you do that, it's quite easy actually.
    – Allan
    Sep 13, 2017 at 14:55

Maxing out the RAM and especially a large, modern SSD are certainly options to consider.

However, the way you described your setup there will be probably quite a bit of cruft accumulated, caused by an upgrade over an existing installation and/or Migration Assistant afterwards.

Before throwing any money at it, you should try how the machine performs with a clean install. Given that you are still on rotating magnetic disks, any external drive to try this approach should not be so drastically different and give you an impression of the changes achievable.

That is radical, takes a while but is also easy. You may also try to analyse, what really causes the slowness in your current setup. If the perceived slowness is in Sierra but not in El Capitan then it stands to reason that there is too much going on behind the scenes. Fresh installs of 10.11 vs 10.12 are not that different in terms of perceived speed on this kind of hardware.

If you are successful with improvements on you current setup and want to keep the hardware: then by all means necessary, go an get an SSD (installed).


Ok. For now I was able to make my machine run fast by cleaning up several things:

  • Clean up my desktop

  • Clean up/backup a lot of hard drive (now having about 40% free space, about 10% more than I had before)

  • Deactivate Time Machine

  • Cleaned up some login items I usually do no use so much, including Dropbox, sync and gdrive.

  • Deactivate effects and transparency on windows (System Preferences > Accessibility > Display)

I don't know if it was one of the previous or all together. I also think that probably there were some background tasks running, probably for indexing, both from the system (Time Machine, Spotlight, file caching, etc..) and from sync or gdrive or I don't know.

Anyway, now it is running really fast again.

  • 1
    I'm glad your iMac is running really fast again, but deactivating Time Machine is really not a good option. I would now try enabling Time Machine again and seeing how your iMac performs after it finishes it's next backup.
    – Monomeeth
    Dec 15, 2017 at 9:54

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