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Bob Switzer Author

Level 1

11 points

Booting off an external drive and not seeing the internal drive

In preparation for upgrading to Catalina I decided to create an external drive running El Capitan so that I can run some old software that will not run on my current system, Mojave and won't run on Catalina. I am using an iMac 27 in. 5K, Late 2014. I have installed the software on the drive and have booted from the drive successfully.

The problem is I don't see the internal drive on the iMac as a drive icon on the El Capitan desktop. Also when I go to System Prefs>StartUp Disk I don't see the iMac drive to switch back to, which I guess is to be expected since it's not showing up on the desktop. I have to shut down the computer and let it boot up on the internal drive. Is there some networking settings that I need to implement that will allow the drive to be seen.

Thanks, Bob

iMac with Retina 5K display, macOS 10.14

Posted on Apr 1, 2020 11:43 AM

Top-ranking reply

Kappy

Level 10

361,855 points

Posted on Apr 1, 2020 12:22 PM

If the Mojave drive in your iMac is formatted APFS, then that is why. El Capitan cannot understand APFS. You should install Mojave on the external drive.

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Booting off an external drive and not seeing the internal drive

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