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The MBR bootstrap code loads and runs (a boot loader- or operating system-dependent) volume boot record code that is located at the beginning of the "active" partition. The volume boot record will fit within a 512-byte sector, but it is safe for the MBR code to load additional sectors to accommodate boot loaders longer than one sector, provided ...
The VBR then loads a second-stage bootloader from another location on the disk. Furthermore, whatever is stored in the first sector of a floppy diskette, USB device, hard disk or any other bootable storage device, is not required to immediately load any bootstrap code for an OS, if ever. The BIOS merely passes control to whatever exists there ...
The boot code in the VBR can assume that the BIOS has set up its data structures and interrupts and initialized the hardware. The code should not assume more than 32 KB of memory to be present for fail-safe operation; [1] if it needs more memory it should query INT 12h for it, since other pre-boot code (such as f.e. BIOS extension overlays, encryption systems, or remote bootstrap loaders) may ...
This enables booting off alternative drives, even when the VBR code ignores the DL value. 0x025 0x1A 1 Reserved; In some MS-DOS/PC DOS boot code used as a scratchpad for the INT 13h current head high byte for the assumed 16-bit word at offset 0x024. Some DR-DOS FAT12/FAT16 boot sectors use this entry as a scratchpad as well, but for different ...
BIOS parameter block. In computing, the BIOS parameter block, often shortened to BPB, is a data structure in the volume boot record (VBR) describing the physical layout of a data storage volume. On partitioned devices, such as hard disks, the BPB describes the volume partition, whereas, on unpartitioned devices, such as floppy disks, it ...
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 ...
Extended boot record. 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 ...
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.