Master boot record
Master boot record A master boot record (MBR) is the first sector ("sector zero") of a data storage device such as a hard disk. It is sometimes used for bootstrapping operating systems, sometimes used for holding a disc's partition table, and sometimes used for uniquely identifying individual disc media; although on some machines it is entirely unused and ignored. In practice, MBR almost always refers to the 512-byte boot sector, or partition sector of a disk partitioned for IBM PC-compatible computers. Due to the broad popularity of PC-compatible computers, this type of MBR is widely used, to the extent of being supported on other types of computer, and incorporated into newer cross-platform standards for bootstrapping and partitioning.