BootMGR

BOOTMGR, short for Windows Boot Manager, is a small system program used by Windows Vista and later to start the operating system. It runs at startup and selects a boot entry from the boot configuration data, then transfers control to the Windows Boot Loader (winload.exe) to continue the boot process. BOOTMGR is involved in presenting boot options, applying the default entry, and enforcing timeouts.

The boot configuration data (BCD) store is central to BOOTMGR’s function. The BCD contains boot-time parameters, a list of installed operating systems, and recovery options. BOOTMGR reads the BCD to determine what to boot and where to load the loader from. If multiple Windows installations or other bootable systems exist, entries can be added or modified to customize the menu and behavior.

Location and architecture: On BIOS/legacy systems, BOOTMGR resides on the system partition (often the System Reserved partition) and reads the BCD from the same location. On UEFI systems, the firmware uses a separate EFI boot manager (bootmgfw.efi) to start the Windows boot process, after which control is handed to the Windows Boot Manager and winload.exe as needed. In all cases, the BCD file is stored on the system partition under a Boot directory.

History and usage: BOOTMGR replaced the older NTLDR boot loader starting with Windows Vista and continues to be used in Windows 7, 8, 10, and 11. It supports multi-boot configurations, including dual-boot setups with other operating systems, by presenting entries that point to alternative loaders or via chain loading.

Troubleshooting: If BOOTMGR is missing or corrupted, the system may display “BOOTMGR is missing.” Recovery typically involves booting from installation media, selecting Repair your computer, and using tools such as bootrec /rebuildbcd, bootrec /fixmbr, and bootrec /fixboot, or restoring the System Reserved partition and BCD.