I made a bootable clone of my iMac with mountain lion using Carbon Copy Cloner. This bootable clone opens fine on the old Mac. I tried to open it on my newer Mac with High Sierra, but when I click on the drive I just get a circle with a bar through it and it doesn't load. Is this because there is a different OS? The reason I want to clone the old hard drive is in case that Mac dies and I would like to be able to access the old data and run the older OS as I have software on it the won't work on the newer OS. Is there a way to do clone that drive so that it loads with mountain lion running on my newer Mac?

  • You can still access the data without booting to the old disk. As answered, to run older programs, you'll need a Virtual Machine. However, you should be able to find modern upgrades, alternatives or equivalents for your apps.
    – benwiggy
    Mar 26, 2020 at 16:27

1 Answer 1


To be absolutely certain we'd need to know precisely which Mac your newer one is, but the general rule is:-

You cannot boot a Mac to an OS older than itself.

The drivers for the yet-to-be-invented hardware simply did not exist in the older OS, so it will not boot from it.

Solutions may be
1. Spare older hardware in case of failure of the original
2. A Virtual Machine made from the older OS - Parallels or VMWare etc.

  • hey thanks - I am trying to boot the older Mac to the newer one. so should that be doable? Mar 26, 2020 at 16:36
  • That gives me no additional information to work from.
    – Tetsujin
    Mar 27, 2020 at 9:06
  • Each mac has an oldest macos and a newest macos that it will boot. I'd say your machine doesn't support that version of macos. Hence the suggestion to get a VM. Mar 27, 2020 at 19:02

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