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Version 1.10 12/01/02 3-1
3
Boot Manager
The EFI boot manager is a firmware policy engine that can be configured by modifying
architecturally defined global NVRAM variables. The boot manager will attempt to load EFI
drivers and EFI applications (including EFI OS boot loaders) in an order defined by the global
NVRAM variables. The platform firmware must use the boot order specified in the global
NVRAM variables for normal boot. The platform firmware may add extra boot options or remove
invalid boot options from the boot order list.
The platform firmware may also implement value added features in the boot manager if an
exceptional condition is discovered in the firmware boot process. One example of a value added
feature would be not loading an EFI driver if booting failed the first time the driver was loaded.
Another example would be booting to an OEM-defined diagnostic environment if a critical error
was discovered in the boot process.
The boot sequence for EFI consists of the following:
• The boot order list is read from a globally defined NVRAM variable. The boot order list
defines a list of NVRAM variables that contain information about what is to be booted. Each
NVRAM variable defines a Unicode name for the boot option that can be displayed to a user.
• The variable also contains a pointer to the hardware device and to a file on that hardware device
that contains the EFI image to be loaded.
• The variable might also contain paths to the OS partition and directory along with other
configuration specific directories.
The NVRAM can also contain load options that are passed directly to the EFI image. The platform
firmware has no knowledge of what is contained in the load options. The load options are set by
higher level software when it writes to a global NVRAM variable to set the platform firmware boot
policy. This information could be used to define the location of the OS kernel if it was different
than the location of the EFI OS loader.
3.1 Firmware Boot Manager
The boot manager is a component in the EFI firmware that determines which EFI drivers and EFI
applications should be explicitly loaded and when. Once the EFI firmware is initialized, it passes
control to the boot manager. The boot manager is then responsible for determining what to load
and any interactions with the user that may be required to make such a decision. Much of the
behavior of the boot manager is left up to the firmware developer to decide, and details of boot
manager implementation are outside the scope of this specification. In particular, likely
implementation options might include any console interface concerning boot, integrated platform
management of boot selections, possible knowledge of other internal applications or recovery
drivers that may be integrated into the system through the boot manager.