Windows® Internals, Sixth Edition, Part 2

If there is more than one boot-selection entry in the BCD, Bootmgr presents the user with the boot-selection menu (if there is only one entry, Bootmgr bypasses the menu and proceeds to launch Winload.exe). Selection entries in the BCD direct Bootmgr to the partition on which the Windows system directory (typically \Windows) of the selected installation resides. If Windows was upgraded from an older version, this partition might be the same as the system partition, or, on a clean install, it will always be the 100-MB hidden partition described earlier.

Entries in the BCD can include optional arguments that Bootmgr, Winload, and other components involved in the boot process interpret. Table 13-2 contains a list of these options and their effects for Bootmgr, Table 13-3 shows a list of BCD options for boot applications, and Table 13-4 shows BCD options for the Windows boot loader.

The Bcdedit.exe tool provides a convenient interface for setting a number of the switches. Some options that are included in the BCD are stored as command-line switches (“/DEBUG”, for example) to the registry value HKLM\SYSTEM\CurrentControlSet\Control\SystemStartOptions; otherwise, they are stored only in the BCD binary format in the BCD hive.

Table 13-2. BCD Options for the Windows Boot Manager (Bootmgr)

BCD Element

Values

Meaning

bcdfilepath

Path

Points to the Boot Configuration Database (usually \Boot\BCD) file on the disk.

displaybootmenu

Boolean

Determines whether the Boot Manager shows the boot menu or picks the default entry automatically.

keyringaddress

Physical address

Specifies the physical address where the BitLocker key ring is located.

noerrordisplay

Boolean

Silences the output of errors encountered by the Boot Manager.

Resume

Boolean

Specifies whether or not resuming from hibernation should be attempted. This option is automatically set when Windows hibernates.

Timeout

Seconds

Number of seconds that the Boot Manager should wait before choosing the default entry.

resumeobject

GUID

Identifier for which boot application should be used to resume the system after hibernation.

displayorder

List

Definition of the Boot Manager’s display order list.

toolsdisplayorder

List

Definition of the Boot Manager’s tool display order list.

bootsequence

List

Definition of the one-time boot sequence.

Default

GUID

The default boot entry to launch.

customactions

List

Definition of custom actions to take when a specific keyboard sequence has been entered.

bcddevice

GUID

Device ID of where the BCD store is located.

Table 13-3. BCD Options for Boot Applications

BCD Element

Values

Meaning

avoidlowmemory

Integer

Forces physical addresses below the specified value to be avoided by the boot loader as much as possible. Sometimes required on legacy devices (such as ISA) where only memory below 16 MB is usable or visible.

badmemoryaccess

Boolean

Forces usage of memory pages in the Bad Page List (see Chapter 10, for more information on the page lists).

badmemorylist

Array of page frame numbers (PFNs)

Specifies a list of physical pages on the system that are known to be bad because of faulty RAM.

baudrate

Baud rate in bps

Specifies an override for the default baud rate (19200) at which a remote kernel debugger host will connect through a serial port.

bootdebug

Boolean

Enables remote boot debugging for the boot loader. With this option enabled, you can use Kd.exe or Windbg.exe to connect to the boot loader.

bootems

Boolean

Used to cause Windows to enable Emergency Management Services (EMS) for boot applications, which reports boot information and accepts system management commands through a serial port.

busparams

String

If a physical PCI debugging device is used to provide FireWire or serial debugging, specifies the PCI bus, function, and device number for the device.

channel

Channel between 0 and 62

Used in conjunction with {debugtype, 1394} to specify the IEEE 1394 channel through which kernel debugging communications will flow.

configaccesspolicy

Default, DisallowMmConfig

Configures whether the system uses memory mapped I/O to access the PCI manufacturer’s configuration space or falls back to using the HAL’s I/O port access routines. Can sometimes be helpful in solving platform device problems.

debugaddress

Hardware address

Specifies the hardware address of the serial (COM) port used for debugging.

debugport

COM port number

Specifies an override for the default serial port (usually COM2 on systems with at least two serial ports) to which a remote kernel debugger host is connected.

debugstart

Active, AutoEnable, Disable