So it is possible that I can get a good deal on a 2012 iMac. The only thing that scares me is the slow 1tb hard drive in it. I searched on how to replace it but it is extremely complicated because the iMac is glued together, I'm not ready to go down that road.

So my idea was to take a SATA3 SSD, put it in a SATA USB 3.0 HDD enclosure and then connect that over USB 3.0 and install MacOS on it.

Q: Is it a good idea to run your OS on an external hard drive? Does anyone have experience with this or alternative solutions?

2 Answers 2


Yes, it's totally fine to install and run macOS on an external HDD/SSD.

Especially since USB 3 you can get the same speed as the internal drive – or even faster in the case of an SSD.

The only downside is the fact that you will have one USB-port permanently occupied. It may also not be as pleasing to one's eye if there's an external drive permanently attached.

Enjoy your new iMac!

  • 1
    Thanks! I dont really care about one usb being blocked, I'm probably going to use a usb hub anyway, and a permanently attached drive doesnt bother me. If it does I will tape it to the back of the iMac or something.
    – Tanonic
    Feb 4, 2017 at 14:23
  • would Thunderbolt be a better option for this set-up?
    – MmmHmm
    Feb 4, 2017 at 14:28
  • 2
    Thunderbolt WOULD be faster but Thunderbolt enclosures are difficult to find and rather expensive. I ended up doing just this but with Firewire 800 as my USB ports are only USB 2. It is faster. Feb 4, 2017 at 14:30
  • 1
    @Mr.Kennedy if USB 3.0 is the bottleneck then yes, go for a thunderbolt drive. I use a TB RAID for really storage. For everything else I use USB 3 drives.
    – oa-
    Feb 4, 2017 at 14:32
  • 1
    USB 3 Supports 5000 MBit/s, FW800 800 MBit/s and USB 2 480 MBit/s. Go for USB 3.
    – oa-
    Feb 4, 2017 at 14:45

21" 2012 imac could be bought with i7. Excellent machine, boosted to 20 gb RAM


  • The spec said the RAM could only be 16gb max, but appears to have headroom to run it. Feb 4, 2017 at 21:21
  • I think the iMac I was offered only has an i5 but I think that is enough for me, I don't need an i7. And for the ram I don't know how much it has but I think since the standard is 8gb, that it is 8gb. 8gb was always enough for me in my desktop and my MBP but another ram stick really isn't expensive so I might upgrade to 16gb
    – Tanonic
    Feb 4, 2017 at 22:45

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