MS-DOS and Windows command line fixboot command
The fixboot command is available in the following Microsoft operating systems.
Writes a new partition boot sector to the system partition. The fixboot command is only available when you are using the Recovery Console.
Drive is where the boot sector will be written. This drive replaces the default drive, which is the system partition of the machine you're logged into.
In the example above, the boot sector would be written to the C: drive.