Bios Parameter Block (BPB) Structure

    The device BPB field is a data structure that describes the current disk
    and its control area.

               Length
    Offset     (bytes)  Description
    ────────────────────────────────────────────────────────────────────────

    NOTE: Offset = offset into boot sector (logical sector zero)

    (0h        0        JMP to boot program, if bootable disk)
    03h        8        System ID
    0Bh        2        Number of bytes per sector
    0Dh        1        Number of sectors per cluster
    0Eh        2        Reserved sectors, beginning at sector 0
    10h        1        Number of copies of file allocation table (FAT)
    11h        2        Maximum number of root directory entries
    13h        2        Total number of sectors
                        For DOS 4.0, set to zero if partition is larger than
                        32MB in which case the dword at offset 20h contains
                        total number of sectors
    15h        1        DOS media descriptor byte
    16h        2        Number of sectors per FAT
    18h        2        Number of sectors per track
    1Ah        2        Number of heads (sides)
    1Ch        4        Number of hidden sectors
    20h        4        For DOS greater than 4.0: total number of sectors if
                        word at offset 13h contains zero
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