Booting from an External Device on Restart

• Connect the external drive or device to the Mac
• Reboot the Mac and after the startup chime hold down the OPTION key during boot until you see the boot selection menu
• Click the external volume to boot from it

Selecting a Different Boot Drive

• Attach the boot drive to the Mac
• Open System Preferences from the  Apple menu and choose “Startup Disk”
• Select the newly connected boot volume from the list, then choose “Restart” or reboot the Mac as normal to start from that disk