Reverting to El Capitan from (current) Catalina

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Reverting to El Capitan from (current) Catalina

I have a new (to me) Imac. It is running on Catalina. I have decided I want to revert to El Capitan. (I have several reasons). It is proving difficult. I have an installation copy of El Capitan on a flash drive, but when I go through the install process I am not given the choice of installing it on my main hard drive. Rather the computer offers to install it on the very flash drive it is coming from. Some have said I should format the computer first. But what if they are wrong, and I can't install El Capitan. Then I won't have a running computer. How, step by step, do I revert to El Capitan. The imac is a 2013 model. Thanks.

iMac 21.5″, macOS 10.15

Posted on Nov 24, 2021 3:58 PM

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HWTech

Level 9

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Nov 24, 2021 7:23 PM in response to bbbacres

You must first erase the whole physical destination drive (or Fusion Drive if so equipped) as GUID partition and MacOS Extended (Journaled), then you should be able to select the new volume as a destination for macOS 10.11. macOS 10.11 does not understand the newer APFS volumes used by macOS 10.13+.

If the iMac has a third party NVMe SSD installed, then you will only be able to install & use macOS 10.13+ since older versions of macOS do not have the necessary NVMe driver.

FYI, whenever you acquire a used computer you should always perform a clean install of the OS by first erasing the whole physical drive before installing the OS.

You can also try booting into Internet Recovery Mode using Command + Option + R to make sure this works as it may give you another option for reinstalling macOS if you have issues using the macOS 10.11 USB installer after erasing the drive.

You should also have frequent and regular backups.

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Reverting to El Capitan from (current) Catalina

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