After you install an earlier version of the Windows operating system on a Microsoft Windows Vista-based computer in a dual-boot configuration, you may experience one of the following issues:

• If you install an earlier version of the Windows operating system on a Windows Vista-based computer, Windows Vista no longer starts. In this case, only the earlier version of the Windows operating system starts.
• If you install an additional instance of Microsoft Windows XP on a computer where Windows XP and Windows Vista are already installed in a dual-boot configuration, you may receive the following error message:

These issues occur because earlier versions of the Windows operating system are incompatible with the new Windows Vista startup method. Windows Vista uses a new Boot Configuration Database (BCD) store. This store contains a boot menu and all the information about operating systems that are installed on the computer. Therefore, a Boot.ini file that is from an earlier version of the Windows operating system cannot be used to start Windows Vista.

In earlier versions of the Windows operating system that run on a basic input/output system (BIOS)-based computer, such as Windows XP, the boot process starts with the system BIOS. The BIOS determines the boot device, and then loads the first physical sector. This physical sector is named the master boot record (MBR). The MBR contains the partition table and the necessary boot execution code. This code searches the partition table to find the active partition and passes control to the boot sector on the active partition. Then, the boot sector on the active partition loads the Ntldr program. The Ntldr program parses the Boot.ini file. This file is used to enumerate the operating systems that are installed.

When Windows Vista starts on a BIOS-based computer, the BIOS loads the MBR and then loads the boot sector. However, boot code loads the new Windows Boot Manager program (Bootmgr). The Windows Boot Manager program parses the binary coded decimal (BCD) Boot.ini file, enumerates the installed operating systems, and then displays the boot menu. If an earlier version of the Windows operating system is installed in a dual-boot configuration with Windows Vista, the Windows Boot Manager program transfers control to the Ntldr program for the earlier version of the Windows operating system. The Windows Boot Manager program does this when you select Windows Vista from the boot menu.

When you install an earlier version of the Windows operating system on a Windows Vista-based computer, Setup overwrites everything from the MBR, the boot sector, and the boot files. Therefore, the earlier version the Windows operating system loses forward compatibility with Windows Vista.

To resolve these issues, follow these steps.

Note You can run the commands in the following procedure by using the command prompt. If you run these commands in Windows Vista, run them at a command prompt that has elevated user rights. To do this, click Start, click Accessories, right-click the command-prompt shortcut, and then click Run as Administrator.

1. Use Bootsect.exe to restore the Windows Vista MBR and the boot code that transfers control to the Windows Boot Manager program. To do this, type the following command at a command prompt: Drive:\boot\Bootsect.exe /NT60 All
   
   In this command, Drive is the drive where the Windows Vista installation media is located.
   
   Note The boot folder for this step is on the DVD drive.
   
   
2. Use Bcdedit.exe to manually create an entry in the BCD Boot.ini file for the earlier version of the Windows operating system. To do this, type the following commands at a command prompt.
   
   Note: In these commands, Drive is the Drive where Windows Vista is installed.
   Drive:\Windows\system32\Bcdedit /create {ntldr} /d "Description for earlier Windows version"
   
   Note: In this command, Description for earlier Windows version can be any text that you want. For example, Description for earlier Windows version can be "Windows XP" or "Windows Server 2003".
   
   
   • Drive:\Windows\system32\Bcdedit /set {ntldr} device partition=x:
     Note: In this command, x: is the Drive letter for the active partition.
     
     
   • Drive:\Windows\system32\Bcdedit /set {ntldr} path \ntldr
   • Drive:\Windows\system32\Bcdedit /displayorder {ntldr} /addlast
     
     
3. Restart the computer.