BIOS Parameter Block (BPB)

        Bytes  Size   Contens
        ────────────────────────────────────────────────────────────────
        00-01  Word   Bytes/sector.
        02     Byte   Sectors/cluster.
        03-04  Word   Reserved sectors (starting at logical sector 0)
        05     Byte   Number of FATs.
        06-07  Word   Number of root dir entries.
        08-09  Word   Total # of sectors.
        0A     Byte   Media descriptor byte.
        0B-0C  Word   Number of sectors/FAT
        0D-0E  Word   Number of sectors per track
        0F-10  Word   Number of tracks
        11-14  DWord  Number of hidden sectors
        15-26         Reserved

        Because DOS 4.0 supports more than 65535 sectors per. drive,
        an extended BPB is introduced. For drives with less than 10000h
        sectors, it looks like the old one, but for larger drives it is
        extended as below. Note that the "Total # of sectors" field at
        08-09 must be zero, for DOS to identify the BPB as an extended
        BPB.

        0D-0E  Word   Number of sectors/track
        0F-10  Word   Number of heads
        11-14  DWord  Number of hidden sectors
        15-18  DWord  Total number of sectors