I've been putting off upgrading from Mojave 10.14 to Catalina as I know I have at least one paid-for 32-bit app which doesn't offer a free upgrade.

This question talks about manually detecting 32-bit apps prior to installation: How can I find out which Mac apps are 32-bit?

But I wondered, when Catalina is installed will it check for such apps and warn me they won't be usable? Further, will it tidy up by removing such apps or will I end up with non-runnable apps to manually clean up?

1 Answer 1


32-bit apps in Mojave should already bring up a warning when you launch them.

You can check what 32-bit apps you have in System Information: Click to open the Apple menu, then hold Option and click on System Information, which appears where 'About This Mac' was.

Then choose 'Applications' from the sidebar, under Software. This will show you whether the app is 64-bit or not. You can sort the list by that column, giving you all the apps in one place.

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Catalina will not remove any apps: it will just leave them in place.

  • How does MacOS know what applications are installed since there's no Windows-style registry, does it just look at everything in the Applications directory or is there more to it?
    – Mr. Boy
    Commented Jul 15, 2020 at 10:17
  • @Mr.Boy iirc there are hidden files - which can (could) be updated when using cmnd-option-p-r which keep track of all sorts of information like which programs open which files etc
    – Solar Mike
    Commented Jul 15, 2020 at 11:12
  • You can get to the same place by taking System Report after clicking About this Mac and selecting applications. Does not seem to show information for all the installed apps though.
    – Solar Mike
    Commented Jul 15, 2020 at 11:19
  • @Mr.Boy You'll notice it takes a short time for the app to collate the information. It's mostly using Spotlight: there is a metadata field for the executable's architectures.
    – benwiggy
    Commented Jul 15, 2020 at 12:00

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