Boot Process: Windows Vista vs. Windows XP

Synopsis
Have you ever noticed what happens inside your hard drive right from the time when you see the manufacturer logo on your screen till you reach the desktop? Today we are gonna learn how it works.
Boot Process: Windows Vista vs. Windows XP

The boot process in Windows Vista differs from Windows XP in where the operating system is located and the way it is initialized.
As with XP the process begins with the BIOS, then moves to the Master Boot Record (MBR). When the MBR has completed its task, the Partition Boot Record (PBR) will take over and look for the boot loader. In XP, the startup code would look for the NTLDR boot loader, whereas in Vista, the new boot is Bootmgr. The Bootmgr loads the Boot Configuration Database (BCD), which, in turn, loads an OS loader boot application (Winload.exe). Finally, the OS loader application is responsible for initializing the kernel.





Two key actions performed by the NTLDR in previous Windows versions have been divided between two components:
  • \Bootmgr: Reads the boot configuration, including device and path locations.
  • \Windows\System32\Winload.exe: Initializes the kernel.
The boot configuration stored by Boot.ini in previous Windows versions is now stored in the BCD, an extensible database located at \Boot\BCD.








The changes in the startup process are significant in the following ways:
  • The boot process can be extended to support other applications, such as other operating systems, diagnostics, WinRE (Windows Recovery Environment), or other versions of the operating system.
  • Only non version-specific components are stored in the root of the active partition, allowing multi-boot installations to share startup files. This means that theoretically Windows Vista could be installed on a machine running some future Windows version with the same boot structure, and it would not break the boot process for that future version.
  • Tool-oriented boot entries (like the Windows Memory Diagnostic tool) offer maintenance options on boot when a previous startup has failed. This new structure makes tools available earlier during the boot process than in previous versions of Windows. The tools will be available even in the event that all OS-specific boot entries are damaged.
What is the BCD Store?

The BCD store contains boot configuration parameters and controls related to how the operating system is started in Windows Vista. These parameters were previously found in the Boot.ini file (in BIOS-based operating systems) or in the nonvolatile RAM (NVRAM) entries (in Extensible Firmware Interface-based operating systems).
Boot.ini in Windows Vista

BCD eliminates the need for Boot.ini in Windows Vista, although Boot.ini will still be present on dual-boot systems for backwards compatibility. Because the BCD boots to the boot environment first instead of NTLDR, the location of NTLDR is not verified unless an operating system other than Windows Vista is chosen.

Windows Vista boots differently from Windows XP, and Boot.ini is no longer used.
The Boot Configuration Data store contains boot configuration parameters and controls how the operating system is started in Windows Vista.








The BCD store can be modified or repaired using several tools, including:
  • SystemPropertiesAdvanced.exe
  • MSconfig.exe
  • WinRE Startup Repair
  • BCDedit.exe
  • Bootrec.exe
To troubleshoot issues with the BCD store, use Bootrec in the Windows Recovery Environment. You will usually reinstall the operating system rather than use BCDedit.
 
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Comments

The biggest problem of all is that when you upgrade from XP to vista the NTLDR file is left in windows old folder and it is not suppose to work in vista but many times vista detects NTLDR file and then vista can not boot. And you recieve error message saying NTLDR file is missing. In that case you can enter Win RE using the DVD and get to command prompt and run bootrec.exe
 
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