MacOS can be launched on Mac in various ways, which we have already written an informative article about. In the same article, we will dwell on Mac startup mode with booting from CD / DVD, USB, or from an external hard drive.
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Starting a Mac with booting from an external drive may be necessary if you need to run another version or copy of macOS, fix any problems, and so on.
To start, the following conditions must be met:
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How to start a Mac from a bootable CD / DVD?
1. Turn on your Mac by pressing the power button or restart your computer if it is already running.
2. Hold down the key WITH on the keyboard and hold until the boot menu appears. The Mac should boot from the CD / DVD installed in the optical drive. You can also click the left mouse button when starting the operating system in order to remove the drive.
You can burn the macOS image to a bootable CD / DVD using “Disk utility“.
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How to boot to Mac from an external USB storage device?
1. Connect a USB flash drive or external hard drive with macOS installed to your Mac (installation instructions).
2. Turn on your Mac by pressing the power button or restart your computer if it is already running.
3. Hold down the key ⌥Option (Alt) on the keyboard and hold until the boot menu appears.
4. Select the desired volume using the mouse, arrow, or trackpad.
Note: If the desired volume is not displayed, wait a few seconds until the Download Manager finishes scanning the mapped drives.
5. Press the key Return (Enter)to boot a Mac from the selected volume.
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How to start a Mac from another hard drive (USB) / choose a default boot disk from macOS system settings?
1. Open the menu → System Settings …
2. Click on the “Boot volume“.
3. From the list of available volumes, select the disk you want to use as the boot disk.
After rebooting macOS or next start? Mac starts the operating system from the selected volume.
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macOS does not boot from an external hard drive, what should I do?
1. Some older external USB drives require additional power. It is possible that it must be connected to an external power source or use a second USB in Mac.
2. Make sure that the external drive is turned on (again, the prerogative of old USB drives).
3. Restore access rights to the disk and correct errors on it.
4. Make sure the drive is formatted with the type of partition GUID selected.
5. Try connecting the external drive to a different USB port.
6. Make sure the external drive is bootable.
7. Connect the drive directly, without using a USB hub.