creating separate, bootable Mojave volume

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creating separate, bootable Mojave volume

My new iMac came with Catalina. It seems that I ought to be able to create a separate volume with Mojave installed and get the choice of booting with either OS when I hold down the Option key at startup. However, App store won't allow me to just download the Mojave installer without telling me my system is too new. If I could do that, I would put the installer on a bootable USB drive and use it to install in my new volume. Is the installer available somewhere other than the App store?

(I've seen suggestions about running Mojave through a virtual machine, but it seems that performance would be compromised.)

iMac 21.5", macOS 10.15

Posted on Feb 27, 2020 5:20 PM

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Answer 1

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D.I. Johnson

Level 7

24,611 points

Feb 27, 2020 5:28 PM in response to lonwright42

Hello, lonwright42.

As I understand it, the EFI in your new iMac will not allow you to install an OS older that the one that it shipped with.

Your best course in this case might be to create a Mojave bootable volume on an external drive like an ssd or hdd and try to boot the iMac with that. You'll probably have to use another machine to create that bootable drive. And it may not work in any case.

As for running Mojave in a vm... I think your new iMac would have no problem doing that without a performance hit.

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Answer 2

babowa

Level 9

78,441 points

Feb 27, 2020 7:35 PM in response to lonwright42

Unless your iMac came with Mojave, you cannot do it.

If you purchased a refurb, it may be possible depending on the original build. I just picked up a 2017 refurbished iMac today and knew that it originally it came with 10.12.4. The Genius humored me and, after two wipes (the first one flashed/wiped the EFI), he installed 10.12.6 from their server. So, I got exactly what I wanted and can always upgrade later if I want to.

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creating separate, bootable Mojave volume

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