Acer Altos MU.R230E.001 - Manual (Page 106)

4 System BIOS 96
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 Floppy disk drive
2 Optical disc drive
3 Removable device
4 Hard drive