A couple of years ago I bought a used macbook pro from a friend of mine, I knew it was a good deal cause the mbp was modified and had very good response and performance, the specs of this mbp are the following (although its in spanish you will get it):

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I love this macbook, firstly cause its 15 inch and I prefer big laptops, secondly cause the performance its good, from a normal web and email browsing session, up to a large xcode programming workspace or a whole 30 min final cut pro video edition.

In the other hand I recently bought a band new 21.5 inch iMac which also seemed like a good deal, my logic in that moment was that if my 2009 second-hand mbp (2.8 GHz core duo) had excellent performance, a 2014 retina iMac (3GHz Intel core i5) would be up to three times faster than my laptop. iMac specs:

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This iMac its always laggy and opening any app takes soooo much time. It constantly freezes and I cant think about having more than 3 apps at the same time, that would be useless.

I dont know exactly what customization the MBP had, guess it was a RAM and video card upgrade next to the 250GB SSD.

My question is, whats the problem with the iMac and what can I do to achieve the same (or better) performance that the mbp?

The SSD is the main difference?

2 Answers 2


Yes, the SSD is the main difference.

Your iMac has a 1TB 5400rpm SATA Hard Drive and this is what’s causing the bottleneck. The MacBook Pro, on the other hand, has a solid state drive that is multiple times faster. So, while the iMac may actually process things faster, loading apps and reading/writing data will be a lot slower. And, if it needs to use hard drive space when it needs more RAM, this will also significantly slow things down.

Achieving the same/better performance

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 instead. You would then use that drive as your main boot volume.

However, you would 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. Thunderbolt models are still quite expensive, but you'll find USB-C / USB 3.1 models at reasonable prices.

NOTE: 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.

  • Amazing tip. I wanted to confirm my SSD theory and you did. Also, the idea of an external drive sounds pretty good cause I was thinking about taking this issue to the apple technical support so they sell me the HDD to SSD migration, but definitely the external its a much practical solution. Jun 8, 2018 at 3:59
  • 1
    The other good things about this approach is you don’t necessarily need to buy a 1TB external SSD, as the main thing is that you have enough space for your macOS installation and all your apps. Another advantage (and what I would do) is use the internal hard drive as storage. So, for example, you can use the internal drive for your big storage items such as your Photos and/or iTunes libraries as they typically take up quite a bit of space. This will still be quicker than what you have now because the system isn't reading/writing from the same drive.
    – Monomeeth
    Jun 8, 2018 at 4:11
  • Hi Karlo, just wondering if you've had a chance to get your hands on an appropriate external SSD yet? If you have any questions just comment below. :)
    – Monomeeth
    Jun 13, 2018 at 7:28
  • Thanks for the follow up, I checked some drives but unfortunately I cant afford one now. When I buy it I sure tell you If there was a change. Jun 13, 2018 at 18:47
  • I bought a 128GB SSD with 450 mb per second speed average and an external hard drive enclousure with USB C type 2, with capacity up to 10gbps transfers. What do you think? Will that work??? Jun 22, 2018 at 3:03

It's not going to work

Avg speed most of SSDs today have -- is around 400-500Mbps

When you plug such SSD external into USB-C of modern iMac, you will most likely have full speed its capable of -- 400/500Mbps.

But it's absolutely insufficient to work with iMac 27" 5K, for instance. Internal Fusion Drive is measuring 800/1100 Mbps, and it's still kinda laggy.


No luck.

The only option you may have is to install proper SSD INSIDE of the Mac.

  • sorry but this doesn't make sense, you are saying a fusion drive which is a hard disk with a 24gb ssd cache is quick than a drive which is all SSD. Apr 6, 2019 at 19:41

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