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| Windows Boot Manager | |
|---|---|
 Windows Boot Manager operating system select menu | |
| Other names | BOOTMGR |
| Developer(s) | Microsoft |
| Operating system | Windows |
| Predecessor | NTLDR |
| Type | Bootloader |
| License | Proprietary |
TheWindows Boot Manager (BOOTMGR) is thebootloader provided byMicrosoft forWindows NT versions starting withWindows Vista andWindows Server 2008. It is the first program launched by theBIOS orUEFI of the computer and is responsible for loading the rest of Windows.[1] It replaced theNTLDR present in older versions of Windows.
Theboot sector or UEFI loads the Windows Boot Manager (a file namedBOOTMGR oneither the system or the boot partition), accesses the Boot Configuration Data store and uses the information to load theoperating system throughwinload.exe orwinresume.exe onBIOS systems, andwinload.efi andwinresume.efi onUEFI systems.[2]
On system withBIOS firmware, the BIOS invokesMBR boot code from ahard disk drive at startup. The MBR boot code and theVBR boot code are OS-specific. In Microsoft Windows, the MBR boot code tries to find anactive partition (the MBR is only 512 bytes), then executes the VBR boot code of an active partition. The VBR boot code tries to find and execute thebootmgr file from an active partition.[3]
On systems withUEFI firmware, UEFI invokesbootmgfw.efi from anEFI system partition at startup, starting the Windows Boot Manager.
Once launched the Windows Boot Manager reads the Boot Configuration Data to determine what operating systems are present and if it should present the user with a menu allowing them to select which operating system to boot. Before Windows Vista, this data was contained inboot.ini.
These menu entries can include:
The operating system is loaded by individual boot loaders for each install of Windows, called the Windows Boot Loader.
The Windows Boot Manager invokeswinload.exe—the operating systemboot loader—to load the operating system kernel executive (ntoskrnl.exe) and coredevice drivers. In that respect, winload.exe is functionally equivalent to the operating system loader function ofNTLDR in prior versions of Windows NT. InUEFI systems, the file is calledwinload.efi and the file is always located at\windows\system32 or\windows\system32\boot.
If the computer has recentlyhibernated, thenbootmgr will instead invokewinresume.exe. In UEFI systems, the file is calledwinresume.efi and is always located at\windows\system32 or\windows\system32\boot.[4]
BCD is a file that is used to store the configuration of Microsoft's Windows Boot Manager. It is the equivalent ofNTLDR'sboot.ini orGNU GRUB'sgrub.cfg.
For UEFI boot, the file is located at/EFI/Microsoft/Boot/BCD on theEFI System Partition. For traditional BIOS boot, the file is at/boot/BCD on the active partition.[5]
Boot Configuration Data is stored in a data file that has the same format asWindows Registry hives and is eventually mounted at registry keyHKEY_LOCAL_MACHINE\BCD00000[6] (with restricted permissions[7]).
Boot Configuration Data (BCD) is afirmware-independentdatabase forboot-time configuration data.[8]
Several command-line tool to edit this file have been made available: bootrec, bcdboot and bcdedit.
| bcdedit | |
|---|---|
| Developer(s) | Microsoft |
| Operating system | Microsoft Windows |
| Type | Command |
| License | Proprietarycommercial software |
| Website | docs |
Boot Configuration Data may be altered using a command-line tool (bcdedit.exe), using theRegistry Editor[6] (regedit.exe), usingWindows Management Instrumentation, or with third-party tools such asEasyBCD, BOOTICE,[9] or Visual BCD Editor.[10]
Boot Configuration Data allows for third-party integration, so anyone can implement tools like diagnostics or recovery options
Syntax BCDEdit /Command [Argument1] [Argument2] ...Key /? command To display detailed help for a particular command, run bcdedit /? command, where command is the name of the command you are searching for more information about. e.g. bcdedit /? createstore Store commands: /createstore Creates a new empty boot configuration data store. The created store is not a system store. /export Export the contents of the system store into a file. This file can be used later to restore the state of the system store. Valid only for the system store. /import Restore the state of the system store by using a backup data file previously generated with /export. This command deletes any existing entries in the system store before the import takes place. Valid only for the system store. /store This option can be used with most BCDedit commands to specify the store to be used. If this option is not specified, then BCDEdit operates on the system store. Running the bcdedit /store command by itself is equivalent to running the bcdedit /enum active command. /sysstore Set the system store device. This only affects EFI-based systems. It does not persist across reboots, and is only used in cases where the system store device is ambiguous. Operating on entries in a store: /copy Make a copy of a specified boot entry in the same system store. /create Create a new entry in the boot configuration data store. If a well-known identifier is specified, then the /application, /inherit, and /device options cannot be specified. If an identifier is not specified or not well known, an /application, /inherit, or /device option must be specified. /delete Delete an element from a specified entry. /mirror Create a mirror of entries in the store. Changing entry options: /deletevalue Delete a specified element from a boot entry. /set Set an entry option value, e.g. bcdedit /set {bootmgr} displaybootmenu yes To display the Advanced Boot Options menu without tapping the [F8] key during boot. List current settings: /enum [type | id] [/v] List entries in a store. Types: ACTIVE, FIRMWARE, BOOTAPP, BOOTMGR, OSLOADER, RESUME, INHERIT, ALL The /enum option is the default value for BCEdit, so running the bcdedit command without options is equivalent to running the bcdedit /enum active command. /v Verbose mode. Usually, any well-known entry identifiers are represented by their friendly shorthand form. Specifying /v as a command-line option displays all identifiers in full. Running the bcdedit /v command by itself is equivalent to running the bcdedit /enum active /v command. Controlling the boot manager: /bootsequence Specifies a one-time display order to be used for the next boot. This command is similar to the /displayorder option, except that it is used only the next time the computer starts. Afterwards, the computer reverts to the original display order. /default Specifies the default entry that the boot manager selects when the timeout expires. /displayorder Specifies the display order that the boot manager uses when displaying boot options to a user. /timeout Specifies the time to wait, in seconds, before the boot manager selects the default entry. /toolsdisplayorder Specifies the display order for the boot manager to use when displaying the Tools menu. Emergency Management Services options: /bootems Enable or disable Emergency Management Services (EMS) for the specified entry. /ems Enable or disable EMS for the specified Operating System boot entry. /emssettings Set the global EMS settings for the computer. /emssettings does not enable or disable EMS for any particular boot entry. Debugging: /bootdebug Enable or disable the boot debugger for a specified boot entry. Although this command works for any boot entry, it is effective only for boot applications. /dbgsettings Specifies or displays the global debugger settings for the system. This command does not enable or disable the kernel debugger; use the /debug option for that purpose. To set an individual global debugger setting, use the bcdedit /setdbgsettings type value command. /debug Enable or disable the kernel debugger for a specified boot entry. /hypervisorsettings Set the hypervisor parameters. Undocumented: /loglevel level [/raw] level is one of the following: t : trace (stdout) i : info (stdout) w : warning (stderr) e : error (stderr) /raw : Display extra details for the device and osdevice fields. Normal display: device partition=\Device\HarddiskVolume2 osdevice partition=C: With /raw device PartEx 2800000 HD MBR Sig:151767d7 osdevice PartEx 3ed200000 HD MBR Sig:151767d7Set up a system partition, repair the boot environment located on the system partition. BCDBoot can create a Boot Configuration Data (BCD) store on the system partition using the latest version of the Windows files.
Syntax BCDBOOT source [/l locale] [/s volume-letter [/f firmware]] [/v] [/vbcd] [/m [{OS_Loader_GUID}]] [/addlast] [/p] [/bcdclean [full]] [/c]Options source The location of the Windows directory to use as the source for copying boot-environment files. /l The locale to use when initialising the BCD store. default = US English. /s Optional. Specifies the volume letter of the system partition. This option should not be used in typical deployment scenarios. Use this setting to specify a system partition when you are configuring a drive that will be booted on another computer, such as a USB flash drive or a secondary hard drive. The default is the system partition identified by the firmware. /v Enable verbose mode. /vbcd Enable BCD Logging. /m If an OS_Loader_GUID is specified, merge the given loader object within the system template to produce a bootable entry. Otherwise, by default, merge only global objects. /d Preserve the existing default Windows Boot entry. /f Used with /S, specifies the firmware type of the target system partition Options for firmware are 'UEFI', 'BIOS', or 'ALL' If you specify 'ALL', BCDBoot will create both the \Boot and the \Efi\Microsoft\Boot directories, and will copy all required boot-environment files for BIOS and UEFI. /addlast Specifies that the Windows Boot Manager firmware entry should be added last. The default behavior is to add it first. Cannot be used with /p. /bcdclean Clean the BCD Store. By default, simply removes any duplicate entries in the BCD. Can be followed by 'full'. In this case, each entry is scanned If the corresponding device for that entry does not exist, the entry is deleted. /p Specifies that the existing Windows Boot Manager firmware entry position should be preserved in the UEFI boot order. If the entry does not exist, a new entry is added in the first position. Cannot be used with /addlast. By default, during an upgrade BCDBoot moves the Windows Boot Manager to be the first entry in the UEFI boot order. /c Specifies that any existing BCD elements should not be migrated. By default, during an upgrade, BCD elements such as debugsettings or flightsigning are preserved.Syntax BOOTREC /FIXMBR Write an MBR to the system partition. BOOTREC /FIXBOOT Writes a new boot sector onto the system partition. BOOTREC /SCANOS Scans all disks for Windows installations and display entries not currently in the BCD store. BOOTREC /REBUILDBCD Scans all disks for Windows installations and provide a choice of which entries to add to the BCD store.
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