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I have a Macbook Pro, 13 inch mid 2012 on which I'm doing a clean install on an external SSD.

I was able to install Mountain Lion which I have upgraded to Sierra 10.12.6. I'm now trying to update to macOS Catalina, the last supported version for this particular hardware but I get the error message "You may not install to this volume because the computer is missing a firmware partition".

I've run Catalina in the past with this exact setup so I know it can work. I'm sure I'm missing a step somewhere or the installation process has changed but I'm stumped.

Any insights would be apprecciated.

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  • Do you have an internal drive? You need to have an internal drive with the appropriate firmware partition to install the OS. If I remember correctly, High Sierra contains various firmware updates that are required for progressing to higher versions. Try upgrading to High Sierra first, then move to Catalina.
    – benwiggy
    Apr 23, 2022 at 11:46
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    Trying to upgrade to High Sierra returned the same error. Plus I know upgrading to Catalina can work with an external SSD since it has worked before for me with this exact setup.
    – Mark K
    Apr 23, 2022 at 12:02
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    The 'jump steps' were always El Capitan, then High Sierra, though I've heard of people more recently being able to skip El Cap. Make sure you got the latest versions of each installer from Apple - support.apple.com/HT211683
    – Tetsujin
    Apr 23, 2022 at 12:44
  • Mark K: How exact? If your Mid 2012 MacBook Pro does not already have the necessary firmware update which allows Catalina to APFS boot, then the upgrade to Catalina will install an update to the firmware. While the process of updating firmware is not well documented by Apple, the assumption is that the update procedure requires a working EFI partition on the internal drive. The update is only installed once. Also, the upgrade software may need to be run from the internal drive. Subsequent installs of Catalina will not further update the firmware and therefore will not have these restrictions. Apr 23, 2022 at 15:55

1 Answer 1

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This link on ifixit describes a problem similar to mine and provides a working solution. I have shared a screenshot of the most relevant section below.

screenshot of working solution

In summary, I created a bootable USB drive containing High Sierra, formatted the target drive into APFS and performed an installation from the USB drive.

Upgrading from High Sierra to Catalina was straightforward from that point.

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    Because links often go awry over time, this would be a more useful answer if it presented the content of the ifixit.com webpage, rather than just the URL. May 5, 2022 at 14:12
  • @DavidSupportsMonica I understand, it is the reason I left a summary of my own steps. But I will edit my answer and provide more information from the shared link.
    – Mark K
    May 5, 2022 at 14:19
  • Very good. Remember you can include in your answer extensive segments of the target URL's text using the "Edit" function followed by selecting the bold quotation mark icon above the text composition box. May 5, 2022 at 14:48

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