External Boot: No joy

Have a new MacBook Pro 16" running Catalina. Last machine was 2012 iMac. The iMac died. Wanted to look at some stuff on a bootable backup of that machine. It was running Mojave. Choosing an alternative back up was once straightforward. I just tried the instructions on "External Boot" from support.apple.com dated April 11 of 2019 and failed miserably. Have been using Macs since they were introduced.

Flummoxed.

Is there a simpler "step 1, step 2, step 3" instruction set to follow than I'm looking at in the article referenced? I'm not seeing how I can select the alternative disk.

Thanks

Posted on Jan 22, 2020 3:00 PM

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6 replies

Niel

Level 10

741,905 points

Jan 22, 2020 3:04 PM in response to WMB

Mojave is too old to start up that Mac model, or any other one which originally shipped with Catalina.

(178192)

macjack

Level 10

111,242 points

Jan 22, 2020 3:21 PM in response to WMB

No Mac has ever been able to run a system that pre-dates the one it ships with. It's the hardware that isn't compatible.

WMB Author

Level 1

11 points

Jan 22, 2020 4:08 PM in response to macjack

After all these years, I did not know that. My iMac was developing bad sectors on its hard drive about the time I finally updated it to Catalina. That’s why I didn’t attempt to update my backup at that moment - couldn’t tell what was going on and didn’t want a cockeyed backup. Just a bunch of coincidences... Thanks for the reply.

Jan 22, 2020 3:19 PM in response to WMB

From what Neil said, I was wrong about what I no longer say here. I also though you'd be able to boot using Mohave from a bootable external drive by changing a security setting in the recovery environment.

WMB Author

Level 1

11 points

Jan 22, 2020 3:10 PM in response to Niel

Holy cow! Isn’t Mojave the most recent OS before Catalina? Yikes.

Jan 23, 2020 3:07 AM in response to WMB

On reflection, I used to know that. I am beginning to remember some of the things I have forgotten because of my very, very extended absence from this community.

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External Boot: No joy