Fixmbr

Fixmbr is a command used in the Windows Recovery Console to repair the Master Boot Record (MBR) of the active boot disk. The MBR is the first sector of the boot drive and contains bootstrapping code and, in many implementations, a partition table. Fixmbr writes a new, standard MBR to the selected disk, which can restore boot capability after corruption or infection.

The command is intended to repair situations where the MBR has become damaged or overwritten by boot sector viruses or misconfigurations. It operates at a low level and does not examine or repair the partitions or the data on them, nor does it test for file system integrity. It is therefore a surgical repair tool focused solely on the boot code.

Usage and cautions: Fixmbr is typically run from the Recovery Console or a similar recovery environment. The user may be prompted to specify the target disk. Using the wrong disk can render a system unbootable or cause data loss on other disks, so correct disk selection is critical. Because it rewrites the MBR, the operation is destructive to the boot sector and should be performed only when necessary.

History and context: Fixmbr was part of the Windows Recovery Console available on older Windows NT-based systems such as Windows XP, Windows 2000, and Windows Server 2003. In modern Windows environments, similar functionality is provided by bootrec.exe with the /fixmbr option in Windows Recovery Environment or WinRE, which handles the MBR repair in newer tooling.