For example : if I want to open "books" application from the first macOS installed, I can see :
"Books 1.4" <---Big Sur.
"Books 1.3" <---Catalina.

How can I "tell" the macOS of Big Sur to ignore everything on the second partition.

I read something about hiding the second partition, but I want to be 10000% sure what I'm doing (trauma from the past)

I prefer elegant solution that tell the macOS:
"hey, all your files are just in this partition, ignore other partitions"

Here is how I can see the Catalina volume from the Big Sur. enter image description here

  • Can't you just unmount the Catalina partition from within Big Sur? How are your disks/partitions layed out?
    – nohillside
    Commented Jul 25, 2021 at 18:18
  • I just read the word "umount" and it's scares me, like it's the "uncle" of format. It's simple 225GB SDD with 2 volumes(partitions?) on AFPS. on each volume/partition I have macOS installed and I switch between them in startup disk preferences. Can you explain in details what I need to do, and what is actually it's doing ? I know it's probably very simple, but I'm afraid to do mistake. tnx Commented Jul 25, 2021 at 18:25
  • btw. I have in Finder "eject" on that volume. but again, I'm not sure EXACTLY what this mean (like USB ejecting ?) Commented Jul 25, 2021 at 18:27
  • 2
    unmount is basically techspeak for eject :-)
    – nohillside
    Commented Jul 25, 2021 at 18:35
  • Asking before doing "eject": After I "eject", how can I "connect" back if I want ? (reverse the operation), Will I still see the -2- volumes on "startup disk" after "eject" ? Commented Jul 25, 2021 at 18:49

1 Answer 1


Assuming you don't need any of the files on the Catalina partition you can just eject it from Finder.

  • I did "eject". but then the Big Sur still show the app from the Catalina, but without icon. So, I wonder, what cause the Big Sur to "see" the Catalina partition and know app from there ? cause "eject" is not enough. If I restart , it's "connect" again to the partition Commented Jul 25, 2021 at 20:01

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