You can run macOS on a Mac in a variety of ways that we have already written an informative article about. In this article, we will focus on Mac startup mode with booting from a USB or an external hard drive.
Starting a Mac with booting from an external disk may be necessary if you need to run another version or copy of macOS, other OS, fix any problems, and so on.
To start the following conditions must be met:
- The computer is based on the Intel system;
- The volume is formatted with the choice of GUID section type;
- Mac OS X v10.4.5 or later is installed on the USB storage device.
How to Boot Mac from an external Hard Drive or USB device?
- Connect a USB flash drive or external hard drive to your Mac.
- Turn on your Mac by pressing the power button or restart your computer if it is already running;
- Hold down the horkey for boots options: Option (Alt) key on the keyboard and hold until the boot menu appears;
- Select the desired volume using the mouse, arrow or trackpad;
- Press the Enter key to boot the Mac from the selected volume.
If Mac won’t boot from USB or volume is not displayed, wait a few seconds for the Download Manager to finish scanning the connected disks or use next tips, if it’s useless here the list of troubleshooting.
macOS does not Boot from an External Drive, what Should I Do?
- 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 on a Mac;
- Make sure the external drive is turned on (again, the prerogative of old USB-drives);
- Restore the disk access rights and correct the errors on it;
- Make sure the disk is formatted with the choice of partition type GUID;
- Try connecting an external drive to another USB port;
- Make sure the external drive is bootable;
- Connect the drive directly, without using a USB hub.