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I have a mid-2012 MacBook Pro that I am newly setting up as my own. I had to use internet recovery to get up and going before installing Mountain Lion. I want to update to the most current OS compatible. With macOS Big Sur having the requisite of OS X 10.9 on, I thought Catalina would be the most current option.


I have one internal(and no external) which was of a single partition(MacOS) and was the startup disk in use when I created a second partition(MacOS 2) to which I installed Mojave. Now, when turned on Mojave runs as default.


Here is what I know:

  • System Preferences>Startup Disk shows two options:
    • System: macOS, 10.8.5 under the DI MacOS
    • System: macOS, 10.14.6 under the DI MacOS 2
  • Mac OS 2
    • Mount Point: /
    • AFPS Volume under Container disk 1-which has 2.15GB-VM and 661 MB- 2 Unmounted
    • Bootable: No
    • 2.8 GB in memory under Other Volumes
  • Mac OS
    • Mount Point: /Volumes/MacOS
    • SATA Internal Physical Volume
    • Bootable: Yes


Here is what I ask:

Is the mount point being / the reason it is what opens upon power on?


Are the files under Mac OS necessary to Startup Mac OS 2?


If not how do I utilize the space formatted as Mac Extended best? Considering I want to update to Big Sur as well as (if possible) securely run Windows 10 for work.




What do I need to change/save(back up) and how to be able to restore my device-OS and Base System included to this point without much if any data usage? To Internet Restore and install Catalina I used over 16 GB of data which I would like to avoid in the future.


Thank you for reading all of this and I am thankful for any assistance!

MacBook Pro 13″, macOS 10.14

Posted on Jan 9, 2021 12:36 AM

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Question marked as Top-ranking reply

Posted on Jan 9, 2021 4:34 PM

The macOS volume which boots by default is set using the Startup Disk System Preferences. If you are dual booting Mountain Lion and Mojave and you want to set Mojave as the default, then you will need to configure the default Startup Disk while booted to Mojave since Mountain Lion doesn't understand the new APFS file system used by Mojave. You can install rEFInd to make it easier to boot between these two operating systems.


I never recommend anyone to split partitions or to dual boot from the internal drive. People always choose the wrong sizes for the partitions and it takes very little to make one or both partitions non-bootable. If a Virtual Machine is not sufficient for using Windows, then you will need to dual boot with Windows, but I definitely do not recommend triple booting. If you need the old version of macOS for some reason, then install the old macOS to an external USB drive instead.


You can archive your downloaded macOS installers. Just create a folder on your Desktop with a name like "macOS_10.14.6_Mojave_Installer_2021-01-09" and copy the installer from the "Applications" folder. Then use Disk Utility to create an image (.dmg) archive file which you can store on an other external drive. For this method you must have access to a working Mac in order to use these archived installers.


Or you just create a bootable macOS USB installer for each OS you want to use and store these USB sticks (a hard drive is recommended over a USB stick since USB sticks can become corrupted more easily and you can store multiple bootable macOS installers on a single drive if you have multiple partitions). This option means if your Mac is unbootable & you don't have access to another Mac, then you may have a bootable installer.


No matter what make sure to have frequent & regular backups for each OS.


Similar questions

1 reply
Question marked as Top-ranking reply

Jan 9, 2021 4:34 PM in response to Bajones7s

The macOS volume which boots by default is set using the Startup Disk System Preferences. If you are dual booting Mountain Lion and Mojave and you want to set Mojave as the default, then you will need to configure the default Startup Disk while booted to Mojave since Mountain Lion doesn't understand the new APFS file system used by Mojave. You can install rEFInd to make it easier to boot between these two operating systems.


I never recommend anyone to split partitions or to dual boot from the internal drive. People always choose the wrong sizes for the partitions and it takes very little to make one or both partitions non-bootable. If a Virtual Machine is not sufficient for using Windows, then you will need to dual boot with Windows, but I definitely do not recommend triple booting. If you need the old version of macOS for some reason, then install the old macOS to an external USB drive instead.


You can archive your downloaded macOS installers. Just create a folder on your Desktop with a name like "macOS_10.14.6_Mojave_Installer_2021-01-09" and copy the installer from the "Applications" folder. Then use Disk Utility to create an image (.dmg) archive file which you can store on an other external drive. For this method you must have access to a working Mac in order to use these archived installers.


Or you just create a bootable macOS USB installer for each OS you want to use and store these USB sticks (a hard drive is recommended over a USB stick since USB sticks can become corrupted more easily and you can store multiple bootable macOS installers on a single drive if you have multiple partitions). This option means if your Mac is unbootable & you don't have access to another Mac, then you may have a bootable installer.


No matter what make sure to have frequent & regular backups for each OS.


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