I have a mid-2017 iMac that we purchased in September to replace our ageing mid-2010 iMac. The thing is this iMac feels slower than our old iMac. My husband and kids complain all the time too, so it’s not just me.

New iMac Specs:

  • Mid-2017 iMac
  • Retina 4K 21.5 inch
  • 3.0GHz quad-core Intel i5 CPU
  • AMD Radeon Pro 555 with 2GB Memory
  • 1TB Hard Drive
  • 8GB RAM
  • macOS Sierra 10.12.6

Old iMac Specs:

  • Mid-2010 iMac
  • 21.5 inch
  • 3.06GHz dual-core Intel i3 CPU
  • ATI Radeon HD 4670 with 256MB Memory
  • 500GB Hard Drive
  • 8GB RAM
  • Mac OS X El Capitan 10.11.6

Obviously the new iMac has equal or better specs all round, so why does it feel so slooow?! Seems to take ages to boot, run apps, etc.

I know I can’t upgrade the hard drive or RAM now, and I can’t run El Capitan, but is there anything else I can do? Reinstall Sierra? Maybe upgrade to High Sierra? Something else?

  • What exactly is slow?
    – mmmmmm
    Jan 23, 2018 at 11:13
  • The base model iMac is slow - but a ram upgrade will help, from the tech reviews I’ve read.
    – OzzieSpin
    Jan 23, 2018 at 17:46
  • 1
    @Mark Booting up is slow, but we can live with that. It's how slow apps open up and then when using apps the system just halts for a few seconds with a beachball every so often, like it's pausing to save or load something in the background. Very annoying! :(
    – elsa.k
    Jan 23, 2018 at 19:36
  • @OzzieSpin It's not the real cheap base model, but it is the base Retina 4K model.
    – elsa.k
    Jan 23, 2018 at 19:37
  • May you give us more info about the hard drive specs?
    – Fez Vrasta
    Jan 23, 2018 at 22:25

1 Answer 1


Why does it feel so slow?

Your iMac has a 1TB 5400rpm SATA Hard Drive and this is what’s causing the bottleneck. Your mid-2010 iMac would have had a 7200rpm Hard Drive. To fix this you really need to address this bottleneck.

The 'easiest' solution

Since your iMac has two Thunderbolt 3 (USB-C) ports that support speeds up to 40 Gbps (via Thunderbolt) and 10 Gbps (via USB 3.1 Gen 2), the easiest solution is to use an external SSD that’s connected via one of these ports and to install macOS on that and use that drive as your main boot volume. However, you need to ensure that:

  • it’s definitely an external SSD (and not just a hard drive)
  • it supports either Thunderbolt or USB-C (i.e. USB 3.1) as its interface

Both of the above are critical if you’re wanting to improve speed. However, you’ll probably find Thunderbolt models are too expensive, so opt for USB-C / USB 3.1. Do not get confused by USB 3 - this is not the same as USB 3.1. And remember, it needs to connect to one of the two Thunderbolt ports (not one of the USB ports).

Some examples of the types of external drives I mean are:

Once you have the drive you want, you will need to install macOS onto it and migrate your data.


  • You don’t necessarily need to buy a 1TB model (although this would be ideal). The main thing is that you have enough space for your macOS installation and all your apps.
  • Once set up and running okay, you can use the internal hard drive as storage. If you opt for a 500GB external SSD instead of a 1TB one, you may want to consider having your Photos and/or iTunes libraries stored on your internal hard drive instead. Maybe also your iOS backups.
  • To install macOS you will need to reformat the drive so that it’s formatted as a OS X Extended (Journaled) drive and that its 'scheme' is GUID Partition Map.
  • While this iMac is not officially upgradable after purchase, it can actually be done. I upgraded the same model before Christmas so that it had an internal SSD for storage and a lot more RAM. However, I’m guessing this isn’t something you’d want to tackle (I wouldn’t recommend it unless you’re very comfortable with the idea of doing it), but if you are I’m more than happy to chat to you about it.

Let me know if you have any questions or would like to chat about doing an internal upgrade.

Case study

Today (24 Jan 2018) I installed macOS Sierra 10.12.6 on an external SSD (specifically a 500GB Samsung T5) and did some comparison tests to try and provide an indicative idea of the type of speed improvements you could expect.

The tests were performed on the same model iMac as yours (i.e. mid-2017 Retina 4k iMac with 8GB RAM, a 3.0 GHz quad-core i5 CPU and a 5400rpm SATA hard drive). Obviously, your results will vary depending on the software/login items/fonts/kernel extensions you have installed.

Below are the results of my testing.

Test 1: Boot up time (to Login Window): 

  Original boot up time: 1m 23s

  New boot up time: 0m 35s

Test 2: Login time (to full Desktop): 

  Original login time: 1m 15s

  New login time: 0m 9s

Test 3: Launch MS Excel:

  Original load time: 0m 8s

  New load time: 0m 3s

Test 4: Launch MS PowerPoint:

  Original load time: 0m 6s

  New load time: 0m 3s

Test 5:Launch MS Word:

  Original load time: 0m 14s

  New load time: 0m 4s

Test 6: Launch Photos app with a 380 GB Photos library:

  Original load time: 1m 23s

  New load time: 0m 39s

Testing notes:

1. macOS and all apps were installed on the external SSD.

2. All tests performed three times and the results averaged.

3. Each time tests were run, they were run after a fresh reboot.

4. For Test 6, although the Photos app was installed on the external SSD, the 380GB Photos library was stored on the internal 5400rpm SATA hard drive.

  • 5
    You're not gonna get a better answer than that. Fair play Mono.
    – Andre
    Jan 23, 2018 at 14:25
  • 1
    @Monomeeth So we'd have to run the whole system from an external drive? Do you know how much this will improve things?
    – elsa.k
    Jan 23, 2018 at 19:38
  • Yes, that's right. Your iMac would use the external SSD as it's Startup drive. Strictly speaking you only need enough capacity on the external SSD for your macOS installation, your apps, etc, so you could opt for an external SSD of only 256GB in size and then use the 1TB drive for general storage of your data. If you go with a portable option (such as the ones I've linked to), then there's no need for a power adapter as your iMac will also be it's power source.
    – Monomeeth
    Jan 23, 2018 at 21:43
  • 1
    As for how much this will improve things, it really depends on your specific setup, although the difference should be quite noticeable. I actually have a Samsung T5 here somewhere, so I'll do some testing today and will update my answer with the results.
    – Monomeeth
    Jan 23, 2018 at 21:47
  • 1
    Great answer! Would you recommend APFS for the external startup SSD after High Sierra?
    – jamix
    Aug 20, 2018 at 12:15

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