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  When it formats a disk, DOS records information about the disk in logical
  sector 0, the DOS boot sector. (See Chapter 5.) As in previous versions,
  DOS version 4 stores information about the size of the disk's sectors,
  clusters, FAT, and root directory in a table called the BIOS parameter
  block (BPB). But DOS version 4 records more information in the disk boot
  sector than do previous DOS versions.