Then the system will launch from that device every time. unless you keep the boot media in the USB port. That won't be a problem since the BIOS will move to the next device in the boot sequence. In the future, your computer will first check the USB port for boot media when starting up. If you do nothing, your computer will go to the next device in the boot sequence list, which will likely be your hard drive.

Stay alert! Depending on your BIOS, you may be prompted with a message to 'Press any key to boot from an external device', and you will only have a few seconds to respond.

The computer will reboot using the new settings, booting from your USB drive.

Save the change and then exit the BIOS Setup.

In that case, you'll need to: Move Hard Drive Devices to the top, Expand to show all hard drive device options, Move the USB device to the top of that hard drive list. NOTE: If you cannot find USB or Removable Devices among the device options, your BIOS may list it under Hard Drive Devices. Move USB to be first in the boot sequence.All available system devices will be displayed in order of their boot priority. Using the arrow keys on your keyboard, select the BOOT tab.When you enter BIOS Setup, the setup utility page will appear.(Depending on the company that created your version of BIOS, a menu may appear.) During the initial startup screen, press ESC, F1, F2, F8, or F10.Press the Power button on your computer.Start by plugging the thumb drive into a USB port. Otherwise, the computer will load from the hard drive as standard. If you're booting from USB media, you must change the BIOS boot order so the USB device is listed first. The boot order tells the machine which devices to search for the software needed to launch the computer and the priority of each device in that search. Then use a Terminal command to install the OS on your USB drive. That's because the BIOS settings include the machine's boot sequence when starting up. To make a bootable USB, you need to download the OS from the App Store. Starting your PC using USB rescue media is not difficult, although it first requires an adjustment in the BIOS (Basic Input Output System).

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