Master boot record: Difference between revisions

A '''master boot record''' ('''MBR''') is a special type of [[boot sector]] atin the veryfirst few beginningblocks of [[disk partitioning|partitioned]] computer [[mass storage device]]s like [[fixed disk]]s or [[removable drive]]s intended for use with [[IBM PC-compatible]] systems and beyond. The concept of MBRs was publicly introduced in 1983 with [[PC DOS 2.0]].

Support for partitioned media, and thereby the master boot record (MBR), was introduced with IBM [[PC DOS]] 2.0 in March 1983 in order to support the 10 MB [[hard disk]] of the then-new [[IBM Personal Computer XT]], still using the [[FAT12]] file system. The original version of the MBR was written by David Litton of IBM in June 1982. The partition table supported up to four ''primary partitions'', of which [[DOS]] could only use one. This did not change when [[FAT16]] was introduced as a new file system with DOS 3.0. Support for an ''[[extended partition]]'', a special primary partition type used as a container to hold other partitions, was added with DOS 3.2, and nested ''logical drives'' inside an extended partition came with DOS 3.30. Since MS-DOS, PC DOS, OS/2 and Windows were never enabled to boot off them, the MBR format and boot code remained almost unchanged in functionality (except some third-party implementations) throughout the eras of DOS and OS/2 up to 1996.