How to Write a New MBR Using Fdisk on SATA Hard Drives

Written by gareth downes-powell
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How to Write a New MBR Using Fdisk on SATA Hard Drives
Use the fdisk command to fix a corrupted master boot record. ( Images)

The master boot record, or MBR, is located on the first sector of a hard drive and used to bootstrap an operating system such as Microsoft Windows. When the PC starts, the BIOS reads the MBR from the hard disk and then executes the machine code instructions to start loading the operating system. If the MBR becomes corrupted, the computer will no longer boot up leaving it unusable, although your data remains on the drive. Boot from the Windows XP CD to access the Windows recovery console, and then use the fdisk command to write a new master boot record.

Skill level:
Moderately Easy

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Things you need

  • Windows XP CD

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  1. 1

    Turn on your computer and insert the Windows XP CD. Press the required key to enter the computer's BIOS; you will see the relevant key for your computer displayed on the computer's POST screen. Make the CD drive the first boot device, and then save the settings and exit the BIOS. The computer will restart and boot from the XP CD.

  2. 2

    Press "R" to start the "Windows Recovery Console" when the set-up screen appears.

  3. 3

    Select the main installation of Windows if you use a dual-boot system. Enter the administrator password when prompted, or just press the "Enter" key if no password is set.

  4. 4

    Type "fdisk /mbr" at the recovery console command prompt to force the fdisk command to write a new MBR to the drive. Partition table information will not be changed.

  5. 5

    Type "exit" at the command prompt to exit the recovery console and restart the computer. Reconfigure the BIOS when the computer restarts to make the hard disk the first boot device.

Tips and warnings

  • Although both commands perform the same function, Microsoft recommends using the "fixmbr" command instead of fdisk.
  • Some BIOS versions protect the MBR and do not allow changes. Disable the MBR protection if the BIOS prevents you writing to the MBR, and then enable again afterwards.
  • Always back up your data if possible before altering the MBR, so you do not lose data in the event of a problem.
  • Some programs add their own special code to the MBR, to enable multiple operating systems for example. The new MBR will overwrite this code.

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