Bootsector of the IBM PC

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Bootsector of the IBM PC

The bootsector of the IBM PC and compatibles is also the partition table of the disk. It is also called Master Boot Record (MBR)


The MBR is 512 bytes large and is the first sector of a disk.

The first FIXME448FIXME bytes contain executable code.

The next FIXME bytes are the partition table.

Final 2 bytes are the signature of the bootsector.


When the signature is valid, the computer's BOOTROM will boot from the disk. To disable it, you have to wipe the signature bytes. You have the read the whole sector (512 bytes) and change only the signature and read back the sector.

A code example:

help requested


More information about the IBM PC bootsector is at

  • please
  • add
  • some links

Back to BootSector, which is also SpinOff