The startup process of Windows NT 6 (Windows Vista and later) differ from the startup process part of previous versions of Windows.
In this article, unless otherwise specified, what is said about Windows Vista also applies to all later NT operating systems. For Windows Vista, the boot sector or UEFI loads the Windows Boot Manager (a file named BOOTMGR on either the system or the boot partition), accesses the Boot Configuration Data store and uses the information to load the operating system. Then, the BCD invokes the boot loader and in turn proceeds to initiate the Windows kernel. Initialization at this point proceeds similarly to previous Windows NT versions.
Windows Vista introduces a complete overhaul of the Windows operating system loader architecture. The earliest known reference to this revised architecture is included within PowerPoint slides distributed by Microsoft during the Windows Hardware Engineering Conference of 2004 when the operating system was codenamed "Longhorn." This documentation mentions that the Windows operating system loader would be undergoing a significant restructuring in order to support EFI and to "do some major overhaul of legacy code." The new boot architecture completely replaces the NTLDR architecture used in previous versions of Windows NT.
Most of the steps that follows the NT kernel being loaded, including kernel initialization and user-space initialization, is kept the same as in earlier NT systems. Refactoring in Winlogon resulted in GINA being completely replaced by Credential Providers and graphical components in Windows Vista and later.
Boot Configuration Data (BCD) is a firmware-independent database for boot-time configuration data. It is used by Microsoft's new Windows Boot Manager and replaces the boot.ini that was used by NTLDR.
Boot Configuration Data is stored in a data file that has the same format as Windows Registry hives and is eventually mounted at registry key [HKEY_LOCAL_MACHINE\BCD00000] (with restricted permissions). For UEFI boot, the file is located at
/EFI/Microsoft/Boot/BCD on the EFI System Partition. For traditional BIOS boot, the file is at
/boot/BCD on the active partition.
|Operating system||Microsoft Windows|
|License||Proprietary commercial software|
Boot Configuration Data may be altered using a command-line tool (bcdedit.exe), using the Registry Editor (regedit.exe), using Windows Management Instrumentation, or with third-party tools such as EasyBCD, BOOTICE, or Visual BCD Editor.
Boot Configuration Data contain the menu entries that are presented by the Windows Boot Manager, just as boot.ini contained the menu entries that were presented by NTLDR. These menu entries can include:
Boot Configuration Data allows for third-party integration, so anyone can implement tools like diagnostics or recovery options.
The BIOS invokes MBR boot code from a hard disk drive at startup. The MBR boot code and the VBR boot code are OS-specific. In Microsoft Windows, the MBR boot code tries to find an active 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 the
bootmgr file from an active partition.
The UEFI invokes
bootmgfw.efi from an EFI system partition at startup.
The Windows Boot Manager invokes
winload.exe—the operating system boot loader—to load the operating system kernel executive (ntoskrnl.exe) and core device drivers. In that respect, winload.exe is functionally equivalent to the operating system loader function of NTLDR in prior versions of Windows NT. In UEFI systems, the file is called
winload.efi and the file is always located at
If the computer has recently hibernated, then
bootmgr will instead invoke
winresume.exe. In UEFI systems, the file is called
winresume.efi and is always located at
With the advent of the new boot manager in Windows Vista, many components have been changed; one is the Advanced Boot Options menu that provides options for advanced boot modes (e.g., Safe Mode). Due to the implementation of fast startup in Windows 8 and up, access to the Advanced Boot Options menu has been disabled by default. However, access is still possible with a BCD modification. These are the possible boot modes:
explorerat the command prompt.
ntbtlog.txt, a file that will log the boot process; listing drivers that loaded and drivers that did not.
The ABO menu is accessible by rapidly pressing or holding the
F8 key before Windows boots. Starting from Windows 8 on UEFI, it can only be accessed by clicking Restart while holding the