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A master boot record (MBR) is a type of boot sector in the first block of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The concept of MBRs was publicly introduced in 1983 with PC DOS 2.0.
The MBR sector may contain code to locate the active partition and invoke its volume boot record. A volume boot record (VBR) is the first sector of a data storage device that has not been partitioned, or the first sector of an individual partition on a data storage device that has been partitioned. It may contain code to load an operating ...
On partitioned devices, it is the first sector of an individual partition on the device, with the first sector of the entire device being a Master Boot Record (MBR) containing the partition table. The code in volume boot records is invoked either directly by the machine's firmware or indirectly by code in the master boot record or a boot manager.
The partition type (or partition ID) in a partition's entry in the partition table inside a master boot record (MBR) is a byte value intended to specify the file system the partition contains or to flag special access methods used to access these partitions (e.g. special CHS mappings, LBA access, logical mapped geometries, special driver access, hidden partitions, secured or encrypted file ...
Note: The column MBR (Master Boot Record) refers to whether or not the boot loader can be stored in the first sector of a mass storage device. The column VBR (Volume Boot Record) refers to the ability of the boot loader to be stored in the first sector of any partition on a mass storage device.
An extended boot record (EBR), [1] or extended partition boot record (EPBR), [note 1] is a descriptor for a logical partition under the common DOS disk drive partitioning system. In that system, when one (and only one) partition record entry in the master boot record (MBR) is designated an extended partition , then that partition can be ...
The Master Boot Record (MBR) partitioning scheme, widely used since the early 1980s, imposed limitations for use of modern hardware. The available size for block addresses and related information is limited to 32 bits.
Boot loaders may face peculiar constraints, especially in size; for instance, on the IBM PC and compatibles, the boot code must fit in the Master Boot Record (MBR) and the Partition Boot Record (PBR), which in turn are limited to a single sector; on the IBM System/360, the size is limited by the IPL medium, e.g., card size, track size.