Windows Boot Manager

The Windows Boot Manager (BOOTMGR) is the bootloader provided by Microsoft for Windows NT versions starting with Windows Vista. It is the first program launched by the BIOS or UEFI of the computer and is responsible for loading the rest of Windows. It replaced the NTLDR present in older versions of Windows. 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 through winload.exe or winresume.exe. On system with BIOS firmware, 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. On systems with UEFI firmware, UEFI invokes bootmgfw.efi from an EFI system partition at startup, starting the Windows Boot Manager. 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. The operating system is loaded by individual boot loaders for each install of Windows, called the Windows Boot Loader. 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.