I have a Late 2015 iMac which has a 2.7 GHz Intel Core i5 processor and 8 GB of memory.

I also have a Mid 2012 MacBook Air which has a 1.8 GHz Intel Core i5 processor and 4 GB of memory.

The iMac uses a Apple HDD in contrast to the MacBook Air's Apple SSD.

However, it seems like the iMac is running much slower than MacBook Air from the day it was bought. It would occasionally show the spinning wheel, when opening files and it would take an average of 20 seconds to open applications.

Q1: Is the HDD/SSD the main cause of this? Since all the other configurations are better than MacBook Air.

Q2: Would its speed improve if I switch the HDD to a SSD?


The examples you've used in your question can be explained by the use of the SSD in the MacBook Air.

In March 2014 I installed a hybrid drive (what Apple calls a 'Fusion' drive) into a late 2008 MacBook Pro. The results of doing this compared to the standard HDD that was installed previously were significant!

Now, remember this was just a hybrid drive NOT an SSD. My tests showed that:

  • bootup time was 16 seconds faster
  • login time was 6 seconds faster
  • launching MS Word was 17 seconds faster

I then tested this against a mid-2011 iMac with a traditional 7200rpm drive and the MacBook Pro was faster! Remember again this was just a hybrid drive NOT an SSD in the MacBook Pro.

One thing you should notice on the iMac though is that the first time you launch an application after booting up it will take longer than subsequent launches (unless you've rebooted again).

So yes, the SSD will explain the difference in the examples you gave, but there will be other tasks that your iMac will perform faster because they rely more on processing power rather than disk read/write times.

Whether you should install an SSD is a matter for you. It'll improve speed generally, but how much will depend on what you use your iMac for.


I found the full results of my testing for the hybrid drive in my late 2008 MacBook Pro. See the table below:

enter image description here

As you can see, the response times also improved by doing a reformat and clean install on the original HDD. However, since you've got a late 2015 iMac I don't imagine you've had enough time to weigh the system down with unnecessary software etc.

The point I guess I'm trying to make is that the answer to your question Is the HDD/SSD the main cause of this? is yes for the examples you gave, but if you have other real life examples that would be good for some context.

  • How can I get a hybrid drive replacement? At an Apple Store? Thanks! – Panda Oct 17 '16 at 4:41
  • Thanks, I'll try to time the launch time for apps and see – Panda Oct 17 '16 at 4:50
  • Just in case you missed it, I added an edit to my answer to include the full results of my hybrid drive test. See my answer here for an explanation of how hybrid/fusion drives work. – Monomeeth Oct 17 '16 at 4:57
  • As far as getting a fusion drive replacement, yes, an Apple Store is the best place as there's quite a bit involved in replacing the internal drive in an iMac. Whether getting one resolves your particular issue(s) will really depend on your situation. But if launching apps and opening files are your main concern, than it'll help. Question: If you didn't have the MacBook Air for comparison, would you have been happy with the iMac? If not, then you may have another issue. – Monomeeth Oct 17 '16 at 4:58
  • Thanks, I was thinking of getting a replacement initially, but just want to find out if it does improves the speed. I'll try to go to my local Apple Store to see if there maybe other problems other than this. It is much slower than my MacBook Air and I would want it to be around the same speed as it. Thanks for your detailed answer, appreciate it! – Panda Oct 17 '16 at 5:04

From what you've written it does not sound like the iMac's sluggishness is caused by the hard drive and I'd wait before swapping it out with a SSD (unless you were going to do that anyway).

It's true that a SSD can read/write faster than a traditional HDD and this should make a machine with the former installed more responsive and feel "zippier" than a comparably spec'd machine equipped with the latter.

However, given that your iMac has double the RAM, a better GPU and a 7200RPM HDD it should be fast and responsive and generally outperform the Air. It should definitely not be taking 20 seconds to launch an application or frequently stalling.

The "spinning beachball" suggests there could be background processes at work on your iMac that are hogging CPU cycles, causing the OS and other applications to struggle.

To check if this is the case Activity Monitor (located by default in
/Applications/Utilities) gives you an overview of the processes that are currently running and how much of the CPU's power they are tying up. This can help pinpoint which applications are using more than their fair share of processing power.

But if your iMac has been sluggish since you bought it, it might easier to back up your data, wipe the drive and do a clean install of the operating system. This could be quicker and less of a hassle than a lengthy troubleshooting process.


To answer your questions directly: Q1: Yes (probably) Q2: Yes (probably)

That is the most likely scenario, but you should check other things as well: start by downloading a program such as black magic design's disk speed tested and check the disk speed on each computer. Likely, you will find that the MacBook Air is significantly slower than the iMac. If this is the case, you will likely be able to speed the computer up by swapping the HDD for an SSD. That being said, on a 2015 iMac, actually doing the replacement may be difficult. If the speed difference isn't that great (less than 2x), look for a different problem.

Please note that I have answered this question to the best of my ability. If I have gotten something wrong, please let me know.


That iMac shipped with a 5400 drive. Yes, I think it's safe to say that's your cause of slowness (assuming you have already run hardware diagnostics etc.) SSDs are significantly faster than rotating drives.

Unfortunately the replacement procedure in those iMacs isn't quite so easy - the screens are glued down, and you have to remove that in order to access the internals. Unless you have some experience, and specialized tools, for taking these apart, I'd recommend you take it to a good shop to replace the stock drive with an SSD.

On the bright side, SSDs are relatively cheap, and b/c it's not such an easy undertaking, I would recommend installing something roomy (at least 512 GB) for future proofing.

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