It is necessary to select primary loading from the hard disk in BIOS for regular computer operation. However, in order to install operating system or run some utilities, you may need to boot a computer from removable drives.
Most new versions of BIOS enable changing the boot sequence by using the so-called boot menu. Press F11 (for AMIBIOS) or Esc (for AwardBIOS) at the moment of primary loading. You might find the other keys in some motherboards of other manufacturers: F8 in motherboards by ASUS, F12 – Gigabyte, F10 – Intel. You can see an exact key from a tip which occurs during the POST procedure.
Then a list of devices from which your computer can boot is displayed on a screen. Select the required device using the cursor buttons and press Enter, then the system will try to boot from it.
Selection of an alternative bootable device affects only the current session and does not modify the boot sequence set in BIOS.