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BIOS parameter block
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<p> In <a href="/facts/Computing/Kghtm9fX">computing</a>, the BIOS parameter block, often shortened to BPB, is a <a href="/facts/Data_structure/yNsNvL1I">data structure</a> in the <a href="/facts/Volume_boot_record/yLef5Tvg">volume boot record</a> (VBR) describing the physical layout of a <a href="/facts/Computer_data_storage/wPHKFpdx">data storage</a> <a href="/facts/Volume_(computing)/g94wpmdC">volume</a>. On partitioned devices, such as <a href="/facts/Hard_disk_drive/kekLSGSE">hard disks</a>, the BPB describes the volume partition, whereas, on unpartitioned devices, such as <a href="/facts/Floppy_disk/rShxfuxa">floppy disks</a>, 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 <a href="/facts/FAT12/uFvpmWxa">FAT12</a> (except for in DOS 1.x), <a href="/facts/FAT16/uFvpmWxa">FAT16</a>, <a href="/facts/FAT32/uFvpmWxa">FAT32</a>, <a href="/facts/High_Performance_File_System/dz2Vgek4">HPFS</a>, and <a href="/facts/NTFS/dryNM3BK">NTFS</a>. 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 <a href="/facts/FAT_BPB/UIMFFkCm">FAT</a> 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). </p>