Acer Altos G540 M2 - Manual (Page 141)

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Boot menu
The Boot menu allows you to set the drive priority during system
boot-up. BIOS setup will display an error message if the drive(s)
specified is not bootable.
By default, the server searches for boot devices in the following order:
1 Optical disc drive
2 Hard drive
3 LAN device with Boot ROM