MBR (Master Boot Record)

In this article, i will explain about the definition of Master Boot Record(MBR). Master Boot Record is a type of boot sector popularized by the IBM Personal Computer.It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk. MBRs are usually placed on storage devices intended for use with IBM PC-compatible systems.


The MBR may be used for one or more of the following:

• Holding a partition table, which describes the partitions of a storage device. In this context the boot sector may also be called a partition sector.
• Bootstrapping an operating system. The BIOS built into a PC-compatible computer loads the MBR from the storage device and passes execution to machine code instructions at the beginning of the MBR.
• Uniquely identifying individual disk media, with a 32-bit disk signature, even though it may never be used by the operating system. 

The master boot record is always located at cylinder 0, head 0, and sector 1, the first sector on the disk.

The master boot record contains the following structures: 

• Master Partition Table: This small table contains the descriptions of the partitions that are contained on the hard disk. There is only room in the master partition table for the information describing four partitions. Therefore, a hard disk can have only four true partitions, also called primary partitions. Any additional partitions are logical partitions that are linked to one of the primary partitions. Partitions are discussed here. One of the partitions is marked as active, indicating that it is the one that the computer should use for booting up.
• Master Boot Code: The master boot record contains the small initial boot program that the BIOS loads and executes to start the boot process. This program eventually transfers control to the boot program stored on whichever partition is used for booting the PC.  

Due to the great importance of the information stored in the master boot record, if it ever becomes damaged or corrupted in some way, serious data loss can be--in fact, often will be--the result.