Which command in the Windows Recovery Environment is specifically used to…

Concept

When a computer's boot record is damaged, Windows cannot start, and the fix is performed offline from the Windows Recovery Environment (WinRE). WinRE ships a dedicated boot-record utility whose job is to rewrite a healthy, Windows-compatible Master Boot Record (MBR) onto the system disk without disturbing the existing partition table. General disk-management, file-system and system-file tools do not write boot records — only the dedicated boot-record tool does.

Application

The MBR lives in the first sector of the disk and hands control to the boot loader at startup; if it is corrupt the machine will not boot. In WinRE the dedicated boot-record tool is Bootrec.exe, and the switch that writes a fresh MBR is:

bootrec /fixmbr

Running this rebuilds the MBR while leaving all partition data intact, which is exactly the repair the question describes.

Contrast

• bootcfg /repair — bootcfg is an older tool for the boot.ini startup configuration of legacy Windows (its actual rebuild switch is /rebuild, not /repair); it does not write the MBR.

• diskpart /mbr — diskpart manages disks, partitions and volumes, but it has no /mbr switch and cannot repair a boot record.

• sfc /repairboot — sfc (System File Checker) scans and restores protected system files; /repairboot is not a real switch and sfc has no role in MBR repair.

• chkdsk /fixboot — chkdsk checks the file system and disk surface; /fixboot is not a valid chkdsk option (the boot-record fix belongs to bootrec, not chkdsk).

Cross-check

Microsoft's own WinRE guidance lists Bootrec.exe with four switches — /fixmbr, /fixboot, /scanos and /rebuildbcd — and documents /fixmbr as the one that writes a Windows-compatible MBR. This confirms the command directly.