1.2 Volume Boot Records
The first sector of a partition is call a Volume Boot Record, or
VBR. The purpose of the volume boot record is to describe a FAT file
system. It does so with the following data:
- DOS Version
- The DOS version string is an 8 byte ASCII text string that identifies the
manufacturer and version of the operating system used to create the file
system.
- Bytes per Sector
- The bytes per sector value represents the number of bytes that are in each
sector of the media that the file system was created on. This is typically
set to 512.
- Sectors per Cluster
- The sectors per cluster value represents the number of physical sectors that
are in each cluster. Clusters are the basic allocation unit of the FAT file
system. See FAT Tables, for more information on clusters.
- Maximum Root Directory Entries
- In the FAT12 and FAT16 file systems, a root directory is a fixed size. This
value represents the number of 32 byte entries the root directory can hold.
FAT32 systems support a variable size root directory, and therefore this field
is meaningless in that file system.
- Media Descriptor Byte
- Some DOS version use the media descriptor byte to determine the characteristics
of the disk drive in which the partition resides. For example hard disk drives
will have a media descriptor byte value of F8h and a 3 1/2" floppy disk may
have a value of F0h.
- Volume Serial Number
- The volume serial number is a 32-bit randomly generated number used to uniquely
identify a file system.
- Volume Label
- The volume label string is an 11 byte ASCII text string that identifies the
file system to DOS. This value is input by the user upon execution of the
format
command.
- File System ID
- The file system ID string is an 8 byte ASCII text string that describes the
file system that resides on that partition. One must be aware, however, that
operating systems do not use this string to determine the file system of the
drive and is essentially useless.