Information Technology Reference
In-Depth Information
Table 8-1: The boot sector contains low-level information about the media's
formatting. These are the fields for a FAT16 volume (Sheet 1 of 2).
Byte
Description
Size
(bytes)
Comments
0
Jump instruction to boot code.
3
For bootable media, byte zero contains
EBh or E9h for an x86 unconditional
jump. Set to 00h for non-bootable media.
3
String that identifies the operating
system that formatted the media
8
Use “MSWIN4.1” for maximum
compatibility.
11
Number of bytes per sector
2
Use 512 for maximum compatibility.
Other allowed values are 1K, 2K, 4K, 8K,
16K, 32K, and 64K.
13
Number of sectors per cluster
1
Allowed values are 1, 2, 4, 8, 16, 32, 64,
and 128. For maximum compatibility,
cluster size must be 32K or less.
14
Number of reserved sectors
2
Must be 1.
16
Number of FATs (identical copies) 1
Use 2 for maximum compatibility.
17
Maximum number of entries in the
root directory
2
Use 512 for maximum compatibility.
19
Total number of sectors if less than
32K
2
The total number of sectors in the media
if less than 32K. The count begins with
the boot sector and includes all regions.
Otherwise zero.
21
Media descriptor
1
Use F8h for non-removable media and
F0h for removable media. This value is
also stored in the first byte of cluster zero
but is generally unused in both locations.
22
Number of sectors per FAT
2
The number of sectors in one FAT.
24
Number of sectors per track
2
Not used in LBA.
26
Number of heads
2
Not used in LBA.
28
Number of hidden sectors
4
The number of hidden sectors that
precede the partition that contains this
FAT volume. Operating-system specific.
Zero if the media doesn't have an MBR
sector.
32
Total number of sectors
4
The total number of sectors in the
volume if 32K or greater. The count
begins with the boot sector and includes
all regions. Otherwise zero.
36
Logical drive number of the
partition
1
Operating-system specific.
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