Windows 7 : Working with Boot Configuration Data

1. Introducing the Windows 7 Boot Environment

Windows computers can use several different processor architectures, several different types of firmware, and several different disk partitioning styles. Generally, computers with 32-bit x86-based processors use the Master Boot Record (MBR) disk partitioning style and BIOS. Computers with Itanium-based IA64 processors use the GUID Partition Table (GPT) disk partitioning style and Extensible Firmware Interface (EFI). Computers with 64-bit x64-based processors use the MBR disk partitioning style and Unified Extensible Firmware Interface (UEFI) which is wrapped around either BIOS or EFI.

Every computer has firmware. Firmware is implemented in motherboard chipsets. Just as Windows has an interface, so does firmware. The interface between the platform firmware and the operating system that handles the startup process. The way a firmware interface works and the tasks it performs depend on the type of firmware interface. Windows computers can use different types of firmware. Generally, computers with 32-bit x86-based processors use BIOS. Computers with Itanium-based IA64 processors use EFI. Computers with 64-bit x64-based processors use UEFI, which is wrapped around either BIOS or EFI. For the purposes of this discussion, a computer that uses UEFI wrapped around BIOS is BIOS-based and a computer that uses UEFI wrapped around EFI is EFI-based.

If you are familiar with the way Windows XP and earlier versions of Windows start, you know these versions of Windows uses Boot.ini to initialize the startup environment and Ntldr to load the operating system. Windows Vista and Windows 7 don’t use these boot facilities. Instead, startup is controlled using the parameters in the BCD data store:

• Entries in the BCD data store identify the boot manager to use during startup and the specific boot applications available.

• Windows Boot Manager controls the boot experience and enables you to choose which boot application is run.

• Boot applications load a specific operating system or operating system version. For example, a Windows Boot Loader application loads Windows 7.

Because BCD abstracts the underlying firmware, you can boot BIOS-based and EFI-based computers in much the same way—just as you can computers based on other firmware models. The BCD store is contained in a file called the BCD registry. On BIOS-based operating systems, the BCD registry file is stored in the \Boot\Bcd file of the hidden System Reserved partition that Windows 7 creates. This partition is visible in the Disk Management MMC Snap-In, but it is not assigned a drive letter by default. On EFI-based operating systems, the BCD registry file is stored on the EFI system partition.

The BCD store contains multiple entries. On a BIOS-based computer, you’ll have one Windows Boot Manager entry. There is only one boot manager, so there is only one boot manager entry. You’ll also have Windows Boot Loader application entries, with one entry for each instance of Windows Vista, Windows 7 or a later version of Windows installed on the computer.

On a computer with Windows XP or earlier operating systems installed in addition to Windows Vista, Windows 7 or later, you’ll have one legacy operating system entry. The legacy entry is not for a boot application. This entry is used to initiate Ntldr and Boot.ini so that you can boot into a pre–Windows Vista operating system. If the computer has more than one pre–Windows Vista operating system, you’ll be able to select the operating system to start after selecting the legacy operating system entry.

2. Working with Boot Configuration Data

Several tools are available to work with and manage the BCD, including the following:

• Startup and Recovery

• System Configuration utility

• BCD Editor

The following sections discuss how these tools are used.

2.1. Using the Startup and Recovery Dialog Box

The Startup and Recovery dialog box enables you to select the default operating system to start if you have multiple operating systems installed on your computer. You can also specify timeout values for operating system selection lists and recovery options.

You can access the Startup and Recovery dialog box by following these steps:

Figure 1. Setting Startup and Recovery options

1. Click Start→Control Panel. In the Control Panel, click System and Security and then click System.

2. In the System utility, click “Advanced system settings” in the left pane.

3. On the Advanced tab of the System properties dialog box, click Settings under Startup and Recovery. This displays the Startup and Recovery dialog box, as shown in Figure 1.

4. Use the “Default operating system” drop-down list to specify the default operating system.

5. Set the timeout interval for the operating system list by selecting the “Time to display list of operating systems” checkbox and specifying a timeout in seconds in the field provided.

6. Set the timeout interval for the recovery options list by selecting the “Time to display recovery options when needed” checkbox and specifying a timeout in seconds in the field provided.

7. Click OK.

2.2. Using the System Configuration Utility

Using the System Configuration utility (Msconfig.exe), you can set the default operating system and control the way your computer starts. For example, you can configure the computer to start in Safe Mode or force the computer to use standard VGA display settings.

Figure 2. The Boot tab in the System Configuration utility

The basic steps for starting and using the System Configuration utility are as follows:

1. Click Start, type msconfig.exe in the Search box and press Enter.

2. Select the Boot tab, as shown in Figure 2.

3. To set the default operating system, click the operating system you want to use and then click “Set as default.”

4. To start the operating system in Safe Mode for troubleshooting, select the “Safe boot” checkbox and then set other troubleshooting options as appropriate.

5. Click OK to apply your changes.

If you are using the System Configuration utility for troubleshooting, you must later remove your selective startup options. After you restart the computer and resolve any problems, access the System Configuration utility again, select Normal Startup on the General tab, and then click OK.

2.3. Using the BCD Editor

The BCD Editor (BCDEdit.exe) is the only tool that gives you direct access to view and manage the BCD data store. You can use BCDEdit to view the entries in the BCD store by following these steps:

1. Click Start, click All Programs, and then click Accessories.

2. Right-click Command Prompt and then select Run As Administrator.

3. Type bcdedit at the command prompt.

Example 1 shows an example of the output from BCDEdit. As the listing shows, the BCD store for this computer has three entries: one for the Windows Boot Manager, one for the Windows Legacy OS Loader, and one for the Windows Boot Loader.

Example 1. Examining the contents of the BCD data store

-------------------- Windows Boot Manager -------------------- identifier {9dea862c-5cdd-4e70-acc1-f32b344d4795} device partition=C: description Windows Boot Manager locale en-US inherit {7ea2e1ac-2e61-4728-aaa3-896d9d0a9f0e} default {1cafd2e9-e035-11dd-bbf6-bdebeb67615f} resumeobject {1cafd2e8-e035-11dd-bbf6-bdebeb67615f} displayorder {1cafd2ed-e035-11dd-bbf6-bdebeb67615f} {1cafd2e9-e035-11dd-bbf6-bdebeb67615f} {360a7720-e6ef-11dc-89b8-84b5c301f2c8} toolsdisplayorder {b2721d73-1db4-4c62-bf78-c548a880142d} timeout 30 Windows Legacy OS Loader ------------------------ Identifier: {ntldr} Type: 10300006 Device: partition=C: Path: \ntldr Description: Earlier Version of Windows Boot debugger: No Windows Boot Loader ------------------- identifier {1cafd2e9-e035-11dd-bbf6-bdebeb67615f} device partition=C: path \Windows\system32\winload.exe description Windows 7 locale en-US inherit {6efb52bf-1766-41db-a6b3-0ee5eff72bd7} recoverysequence {1cafd2f0-e035-11dd-bbf6-bdebeb67615f} recoveryenabled Yes osdevice partition=C: systemroot \Windows resumeobject {1cafd2e8-e035-11dd-bbf6-bdebeb67615f} nx OptIn

The Windows Boot Loader entry has parameters that track the status of the no execute (NX) policy, integrity checking, kernel debugger mode, and Emergency Management Services (EMS). Although the Windows Boot Manager, Windows Legacy OS Loader, and Windows Boot Loader are the primary types of entries that control startup, the BCD also stores information about preoperating system boot environment utilities and settings. To view the BCD entries for utilities and settings, use the following command line:

bcdedit /enum all /v

This command line enumerates all BCD entries, regardless of their current state, and lists them in Verbose Mode. Example 2 shows the verbose entries. It is important to note that Verbose Mode provides the actual value of the GUIDs needed to manipulate entries in the BCD data store.

Example 2. Viewing extended BCD entries

Windows Boot Manager -------------------- identifier {9dea862c-5cdd-4e70-acc1-f32b344d4795} device partition=C: description Windows Boot Manager locale en-US inherit {7ea2e1ac-2e61-4728-aaa3-896d9d0a9f0e} default {1cafd2e9-e035-11dd-bbf6-bdebeb67615f} resumeobject {1cafd2e8-e035-11dd-bbf6-bdebeb67615f} displayorder {1cafd2ed-e035-11dd-bbf6-bdebeb67615f} {1cafd2e9-e035-11dd-bbf6-bdebeb67615f} {360a7720-e6ef-11dc-89b8-84b5c301f2c8} toolsdisplayorder {b2721d73-1db4-4c62-bf78-c548a880142d} timeout 30 Windows Boot Loader ------------------- identifier {1cafd2e9-e035-11dd-bbf6-bdebeb67615f} device partition=C: path \Windows\system32\winload.exe description Windows 7 locale en-US inherit {6efb52bf-1766-41db-a6b3-0ee5eff72bd7} recoverysequence {1cafd2f0-e035-11dd-bbf6-bdebeb67615f} recoveryenabled Yes osdevice partition=C: systemroot \Windows resumeobject {1cafd2e8-e035-11dd-bbf6-bdebeb67615f} nx OptIn Windows Boot Loader ------------------- identifier {1cafd2e0-e035-11dd-bbf6-bdebeb67615f} device ramdisk=[C:]\Recovery\1cafd2e0-e035-11dd-bbf6-bdebeb6761 5f\Winre.wim,{1cafd2e1-e035-11dd-bbf6-bdebeb67615f} path \windows\system32\winload.exe description Windows Recovery Environment inherit {6efb52bf-1766-41db-a6b3-0ee5eff72bd7} osdevice ramdisk=[C:]\Recovery\1cafd2e0-e035-11dd-bbf6-bdebeb6761 5f\Winre.wim,{1cafd2e1-e035-11dd-bbf6-bdebeb67615f} systemroot \windows nx OptIn winpe Yes Resume from Hibernate --------------------- identifier {1cafd2e8-e035-11dd-bbf6-bdebeb67615f} device partition=C: path \Windows\system32\winresume.exe description Windows Resume Application locale en-US inherit {1afa9c49-16ab-4a5c-901b-212802da9460} filedevice partition=C: filepath \hiberfil.sys debugoptionenabled No Windows Memory Tester --------------------- identifier {b2721d73-1db4-4c62-bf78-c548a880142d} device partition=C: path \boot\memtest.exe description Windows Memory Diagnostic locale en-US inherit {7ea2e1ac-2e61-4728-aaa3-896d9d0a9f0e} badmemoryaccess Yes Windows Legacy OS Loader ------------------------ identifier {466f5a88-0af2-4f76-9038-095b170dc21c} device unknown path \ntldr description Earlier Version of Windows custom:45000001 1 custom:47000005 301989892 EMS Settings ------------ identifier {0ce4991b-e6b3-4b16-b23c-5e0d9250e5d9} bootems Yes Debugger Settings ----------------- identifier {4636856e-540f-4170-a130-a84776f4c654} debugtype Serial debugport 1 baudrate 115200 RAM Defects ----------- identifier {5189b25c-5558-4bf2-bca4-289b11bd29e2} Global Settings --------------- identifier {7ea2e1ac-2e61-4728-aaa3-896d9d0a9f0e} inherit {4636856e-540f-4170-a130-a84776f4c654} {0ce4991b-e6b3-4b16-b23c-5e0d9250e5d9} {5189b25c-5558-4bf2-bca4-289b11bd29e2} Boot Loader Settings -------------------- identifier {6efb52bf-1766-41db-a6b3-0ee5eff72bd7} inherit {7ea2e1ac-2e61-4728-aaa3-896d9d0a9f0e} {7ff607e0-4395-11db-b0de-0800200c9a66} Hypervisor Settings ------------------- identifier {7ff607e0-4395-11db-b0de-0800200c9a66} hypervisordebugtype Serial hypervisordebugport 1 hypervisorbaudrate 115200 Resume Loader Settings ---------------------- identifier {1afa9c49-16ab-4a5c-901b-212802da9460} inherit {7ea2e1ac-2e61-4728-aaa3-896d9d0a9f0e} Device options -------------- identifier {1cafd2dd-e035-11dd-bbf6-bdebeb67615f} description Ramdisk Options ramdisksdidevice partition=C: ramdisksdipath \Recovery\1cafd2dc-e035-11dd-bbf6-bdebeb67615f\boot.sdi Device options -------------- identifier {1cafd2e1-e035-11dd-bbf6-bdebeb67615f} description Ramdisk Options ramdisksdidevice partition=C: ramdisksdipath \Recovery\1cafd2e0-e035-11dd-bbf6-bdebeb67615f\boot.sdi

As you can see from the listing, there are a number of additional entries. Each entry has a specific purpose, and lists values that you can set, including the following:

Recovery Environment

In the Windows Boot Loader entries, you’ll find entries that have a description of “Windows Recovery Environment.” The Windows Recovery Environment is a custom preinstallation environment that includes components for recovery and startup troubleshooting. To enable rapid recovery, the Windows Recovery Environment (Windows RE) is installed with Windows 7 automatically. Normally, Windows RE is installed on a hard disk partition other than the one containing the Windows installation. This ensures that Windows RE is separate from the operating system.

Resume from Hibernate

The Resume from Hibernate entry shows the current configuration for the resume feature in Windows 7. The preoperating system boot utility that controls resume is Winresume.exe, which in this example is stored in the C:\Windows\system32 folder. The hibernation data, as specified in the filepath parameter, is stored in the Hiberfil.sys file in the root folder on the filedevice (c: in this example). Because the resume feature works differently if the computer has Physical Address Extension (PAE) and debugging enabled, these options are tracked by the PAE and Debugoptionenabled parameters.

Windows Memory Tester

The Windows Memory Tester entry shows the current configuration for the Windows Memory Diagnostics utility. The preoperating system boot utility that controls memory diagnostics is Memtest.exe, which in this example is stored in the \boot folder of the hidden System Reserved partition. Because the memory diagnostics tool is designed to detect bad memory by default, the badmemoryaccess parameter is set to yes by default.

EMS Settings

The EMS Settings entry shows the configuration used when booting with Emergency Management Services. Individual Windows Boot Loader entries control whether EMS is enabled.

Debugger Settings

The Debugger Settings entry shows the configuration used when booting with the debugger turned on. Individual Windows Boot Loader entries control whether the debugger is enabled. When debug booting is turned on, Debugtype sets the type of debugger as SERIAL, 1394, or USB. With SERIAL debugging, Debugport specifies the serial port being used as the debugger port and Baudrate specifies the baud rate to be used for debugging. With 1394 debugging, you can use Channel to set the debugging channel. With USB debugging, you can use Targetname to set the USB target name to be used for debugging.