The Windows Boot Manager (BOOTMGR) is the bootloader provided by

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

for

Windows NT Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Original ...

versions starting with

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

and

Windows Server 2008 Windows Server 2008, codenamed "Longhorn Server" (alternatives: "Windows Vista Server" or "Windows Server Vista"), is the seventh major version of the Windows NT operating system produced by Microsoft to be released under the Windows Server b ...

. It is the first program launched by the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

UEFI Unified Extensible Firmware Interface (UEFI, as an acronym) is a Specification (technical standard), specification for the firmware Software architecture, architecture of a computing platform. When a computer booting, is powered on, the UEFI ...

of the computer and is responsible for loading the rest of Windows. It replaced the

NTLDR NTLDR (abbreviation of ''NT loader'') is the boot loader for all releases of Windows NT operating system from 1993 with the release of Windows NT 3.1 up until Windows XP and Windows Server 2003. From Windows Vista onwards it was replaced by the B ...

present in older versions of Windows. The

boot sector A boot sector is the disk sector, sector of a persistent data storage device (e.g., hard disk, floppy disk, optical disc, etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed by a computer system's bui ...

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 An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

through winload.exe or winresume.exe on

systems, and winload.efi and winresume.efi on

systems.

Launching

On system with

firmware, the BIOS invokes MBR boot code from a

hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...

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. On systems with

firmware, UEFI invokes bootmgfw.efi from an EFI system partition at startup, starting the Windows Boot Manager.

Operation

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 in . These menu entries can include: * Options to boot Windows Vista and later by invoking winload.exe. * Options to resume Windows Vista and later from hibernation by invoking winresume.exe. * Options to boot a prior version of the Windows NT family by invoking its NTLDR. * Options to load and to execute a volume boot record.

Operating system loading

The operating system is loaded by individual boot loaders for each install of Windows, called the Windows Boot Loader.

winload.exe

The Windows Boot Manager invokes winload.exe—the operating system

boot loader A bootloader, also spelled as boot loader or called bootstrap loader, is a computer program that is responsible for booting a computer and booting an operating system. If it also provides an interactive menu with multiple boot choices then it's o ...

—to load the operating system kernel executive ( ntoskrnl.exe) and core

device drivers In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabli ...

. In that respect, winload.exe is functionally equivalent to the operating system loader function of

in prior versions of Windows NT. In

systems, the file is called winload.efi and the file is always located at \windows\system32 or \windows\system32\boot.

winresume.exe

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 \windows\system32 or \windows\system32\boot.

Boot Configuration Data

Boot Configuration Data (BCD) is a

firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...

-independent

database In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...

for boot-time configuration data. It is used by Microsoft's Windows Boot Manager and replaces the

boot.ini NTLDR (abbreviation of ''NT loader'') is the Booting, boot loader for all releases of Windows NT operating system from 1993 with the release of Windows NT 3.1 up until Windows XP and Windows Server 2003. From Windows Vista onwards it was replaced b ...

that was used by

. Boot Configuration Data is stored in a data file that has the same format as

Windows Registry The Windows Registry is a hierarchical database that stores low-level settings for the Microsoft Windows operating system and for applications that opt to use the registry. The kernel, device drivers, services, Security Accounts Manager, a ...

hives and is eventually mounted at registry key (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.

bcdedit

Boot Configuration Data may be altered using a command-line tool (bcdedit.exe), using the Registry Editor (regedit.exe), using

Windows Management Instrumentation Windows Management Instrumentation (WMI) is a set of extensions to the Windows Driver Model that provides an operating system interface through which instrumented components provide information and notification. WMI is Microsoft's implementatio ...

, or with third-party tools such as EasyBCD, BOOTICE, or Visual BCD Editor. Boot Configuration Data allows for third-party integration, so anyone can implement tools like diagnostics or recovery options