In
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...
, the BIOS parameter block, often shortened to BPB, is a
data structure
In computer science, a data structure is a data organization, management, and storage format that is usually chosen for Efficiency, efficient Data access, access to data. More precisely, a data structure is a collection of data values, the rel ...
in the
volume boot record (VBR) describing the physical layout of a
data storage
Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are cons ...
volume
Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...
. On partitioned devices, such as
hard disks, the BPB describes the volume partition, whereas, on unpartitioned devices, such as
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined ...
s, it describes the entire medium. A basic BPB can appear and be used on any partition, including floppy disks where its presence is often necessary; however, certain filesystems also make use of it in describing basic filesystem structures. Filesystems making use of a BIOS parameter block include
FAT12 (except for in DOS 1.x),
FAT16,
FAT32
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
,
HPFS, and
NTFS
New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred f ...
. Due to different types of fields and the amount of data they contain, the length of the BPB is different for FAT16, FAT32, and NTFS boot sectors.
(A detailed discussion of the various FAT BPB versions and their entries can be found in the
FAT article.) Combined with the 11-byte data structure at the very start of volume boot records immediately preceding the BPB or EBPB, this is also called FDC descriptor or extended FDC descriptor in ECMA-107 or ISO/IEC 9293 (which describes FAT as for flexible/floppy and optical disk cartridges).
FAT12 / FAT16
DOS 2.0 BPB
Format of standard DOS 2.0 BPB for
FAT12 (13 bytes):
DOS 3.0 BPB
Format of standard DOS 3.0 BPB for
FAT12 and
FAT16 (19 bytes), already supported by some versions of MS-DOS 2.11:
DOS 3.2 BPB
Format of standard DOS 3.2 BPB for
FAT12 and
FAT16 (21 bytes):
DOS 3.31 BPB
Format of standard DOS 3.31 BPB for
FAT12,
FAT16 and
FAT16B (25 bytes):
DOS 3.4 EBPB
Format of PC DOS 3.4 and OS/2 1.0-1.1 Extended BPB for
FAT12,
FAT16 and
FAT16B (32 bytes):
FAT12 / FAT16 / HPFS
DOS 4.0 EBPB
Format of DOS 4.0 and OS/2 1.2 Extended BPB for
FAT12,
FAT16,
FAT16B and
HPFS (51 bytes):
FAT32
DOS 7.1 EBPB
Format of short DOS 7.1 Extended BIOS Parameter Block (60 bytes) for
FAT32
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
:
Format of full DOS 7.1 Extended BIOS Parameter Block (79 bytes) for
FAT32
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
:
NTFS
Format of Extended BPB for
NTFS
New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred f ...
(73 bytes):
exFAT BPB
exFAT does not use a BPB in the classic sense. Nevertheless, the
volume boot record in sector 0 is organized similarly to BPBs.
See also
*
BPB formats in the FAT file systems
*
MDBPB
DriveSpace (initially known as DoubleSpace) is a disk compression utility supplied with MS-DOS starting from version 6.0 in 1993 and ending in 2000 with the release of Windows Me. The purpose of DriveSpace is to increase the amount of data the ...
(
Microsoft DoubleSpace BPB)
References
Further reading
* — a description of BPBs, from version 2.0 to version 7.0
* — In the "processing the BIOS parameter block" section the authors describe the evolution of the BIOS parameter block from the MS-DOS version 2.0 BPB to the PC DOS version 4.0 BPB, and label each field with the DOS version that introduced it.
* — Figure 4.3 contains a diagram of the version 4.0 BPB and states that the layout of BPBs "is not defined by Microsoft and can vary with different vendors". At the time that the book was written, this was true. Microsoft first publicly documented the BPB structure in the OS/2 Developers' Toolkit.
* — Verstak reverse engineers the BIOS parameter block. The paper contains several errors. One such is its statement that "the presence of the EBPB in FAT32 is not documented by Microsoft". See:
** — Microsoft documents a version 4.0 BPB and a new "FAT32 BIOS Parameter Block (BPB)" (a version 7.0 BPB) for DOS-Windows 98 that is "larger than a standard BPB", has an "identical structure to a standard BPB", but that also "includes several extra fields".
** — Microsoft documents extended BPBs on both FAT16 and FAT32 volumes. It also documents BPBs on NTFS volumes.
* — The table "BPB and Extended BPB Fields on NTFS Volumes" describes BPBs on NTFS volumes. The descriptions of several fields contradict those given in the Windows 2000 Resource Kit.
* — an issue that affects BPBs
*
* — on the misuse of OEM labels and Microsoft's Volume Tracker
*
*
*
*
*
* {{cite newsgroup , title=Evil :) DOS6 FAT , author-first=Jen , author-last=Kilmer , date=2013-05-21 , newsgroup=comp.os.os2.misc , url=https://groups.google.com/forum/?hl=la#!msg/comp.os.os2.misc/dxxRtZ_V-fU/YVvnukmtfvAJ , access-date=2019-07-29 , url-status=live , archive-url=https://web.archive.org/web/20220529153802/https://groups.google.com/g/comp.os.os2.misc/c/dxxRtZ_V-fU/m/YVvnukmtfvAJ , archive-date=2022-05-29
BIOS
DOS technology