The boot disk is the partition from which, when the computer is turned on, files of a specific operating system will be loaded. In the case of a Mac, you can change the assignment of partitions almost on the fly, following a simple instruction.
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How to set the default boot disk
one. Open System settings. How to call System settings using hotkeys, read here.
2. Click on a section Boot volume.
3. Click on the padlock icon and enter the Administrator password.
4. Mark the partition that you have chosen as bootable. Click Reload.
5. From now on and until further changes are made, the system will always automatically boot from the specified section.
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How to Change Your Startup Disk Without Booting macOS
one. Restart your Mac and hold down the button during the process Option (Alt) on keyboard.
2. Wait for the appearance download manager.
3. On the menu Dispatcher select the desired section and press the key return (Enter).
4. After restarting the computer, the system will boot from the partition specified by default.
The option with the choice of the boot partition in the system settings is designed for stable, measured work, the quick change of the boot disk is useful for those who are passionate about testing and fine-tuning new products.