Boot Manager
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DriverOrder list is used by the firmware’s boot manager as the default load order for EFI
drivers that it should explicitly load.
17.3 Boot Option Variables Default Behavior
The default state of globally-defined variables is firmware vendor specific. However the boot
options require a standard default behavior in the exceptional case that valid boot options are not
present on a platform. The default behavior must be invoked any time the BootOrder variable
does not exist or only points to non-existent boot options.
If no valid boot options exist, the boot manager will enumerate all removable EFI media devices
followed by all fixed EFI media devices. The order within each group is undefined. These new
default boot options are not saved to non volatile storage. The boot manger will then attempt to
boot from each boot option. If the device supports the SIMPLE_FILE_SYSTEM protocol then
the removable media boot behavior (see paragraph 17.4.1.1) is executed. Otherwise the firmware
will attempt to boot the device via the LOAD_FILE protocol .
It is expected that this default boot will load an operating system or a maintenance utility. If this is
an operating system setup program it is then responsible for setting the requisite environment
variables for subsequent boots. The platform firmware may also decide to recover or set to a
known set of boot options.
17.4 Boot Mechanisms
EFI can boot from a device using the SIMPLE_FILE_SYSTEM protocol or the LOAD_FILE
protocol. A device that supports the SIMPLE_FILE_SYSTEM protocol must materialize a file
system protocol for that device to be bootable. If a device does not wish to support a complete file
system it may produce a LOAD_FILE_PROTOCOL which allows it to materialize an image
directly. The Boot Manager will attempt to boot using the SIMPLE_FILE_SYSTEM protocol
first. If that fails, then the LOAD_FILE_PROTOCOL will be used.

17.4.1 Boot via Simple File Protocol

When booting via the SIMPLE_FILE_SYSTEM protocol, the FilePath will start with a device
path that points to the device that “speaks” the SIMPLE_FILE_SYSTEM protocol. The next part
of the FilePath will point to the file name, including sub directories that contain the bootable
image. If the file name is a null device path, the file name must be discovered on the media using
the rules defined for removable media devices with ambiguous file names (see paragraph 17.4.1.1).
The format of the file system specified by EFI is contained in Chapter 16. While the firmware must
produce a SIMPLE_FILE_SYSTEM protocol that understands the EFI file system, any file system
can be abstracted with the SIMPLE_FILE_SYSTEM protocol interface.

17.4.1.1 Removable Media Boot Behavior

On a removable media device it is not possible for the FilePath to contain a file name,
including sub directories. The FilePath is stored in non volatile memory in the platform and can
not possibly be kept in sync with a media that can change at any time. A FilePath for a