How to Boot a MacBook Air From a USB External Drive

By Daniel Barrows

Although the MacBook Air comes with OS X pre-installed, you may wish to experiment with alternative operating systems or test-drive newer versions of Apple's operating system before committing to an upgrade. One solution is to install the operating system onto an external drive and use that device as your boot volume. Apple has made this process relatively simple; once you have installed necessary software on the device, you have two options for selecting it as a boot volume: the “Startup Disk” control panel and the “Startup Manager” window, accessible on startup.

Things You'll Need

  • System software installation disc(s)
  • External USB hard drive
  • USB cable

Installation and Configuration

Step 1

Shut down your MacBook Air and connect the USB external drive to an unused USB port. Turn your laptop back on and insert the installation CD for the system software you wish to use when booting from the external drive. Follow the onscreen instructions; when prompted for a destination drive, choose the option that corresponds to your external drive. After installation, reboot your computer if prompted.

Step 2

Log into the MacBook's default operating system (“OS X”) as normal. Open the “Apple” menu, located in the upper-left corner of your desktop. Select the option labeled “System Preferences.”

Step 3

Click on the icon labeled “Startup Disk.” Click on the system folder located on your external hard drive; this will set that volume as your default drive to boot from when you start your MacBook Air in the future. Click the “Restart” button to reboot your computer using the new system volume.

On-startup Selection

Step 1

Turn on your MacBook Air and hold down the “Option” key; a window labeled “Startup Manager” will appear.

Step 2

Use the arrow keys to select the volume you wish to boot from; this selection will not change your default boot volume settings.

Step 3

Press the “Return” key to confirm your selection and boot from the external device.

Tips & Warnings

  • You may purchase an external USB hard drive for your MacBook Air directly from Apple's website; see “Resources” below.
  • The USB port on your MacBook Air is located in a hidden hatch on the underside of the device, by the right edge.
  • Do not shut down your computer or disconnect the external hard drive while installing the system software.
  • You may be prompted to format the external drive prior to installing your system software; this will erase all data stored on the drive. If you wish to backup certain data, cancel the installation, reboot as normal and transfer the desired files onto a separate device (or burn them on to a CD-RW or DVD-RW disc).