Partition Mojave HD to run Sierra

Started 5 months ago | Discussions thread
silentstorm Senior Member • Posts: 1,486
Re: Easiest method

JohnNewman wrote:

silentstorm wrote:

If your laptop is really the old 17", just removed the drive and buy a new SSD SATA drive.

Put in the new SSD drive and plug in the Sierra installer USB. Install should be a breeze from here.

Get an external enclosure for the Mojave drive. Use it as an external boot drive if u need to use Mojave OS.

This is by far the simplest and easiest method for getting back Sierra OS & no need to reinstall everything again in Mojave.

Thanks for your input. I’m fine with Mojave for just about everything apart from this one application that is actually on the 17”‘s HD. So could I remove this HD from the old machine as you suggest, put in an external enclosure and boot my MacBook Air from there if it was connected by USB?

If that worked I could carry on using my MBAir as normal and just attach the old (enclosed) HD when needed?

Thanks again,


If the Air is running Mojave, I don't think it will boot into Sierra external.  You can try that though.  If the Air has a physical drive and not soldered type, you could remove it and use it as an external Mojave drive on your old 17" Sierra laptop.

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