Appendix D: FAT32 Boot Sector Layout

OFFSET LOCATION	# OF BYTES	IDENTIFIER	NOTES
00	3	Jumpcode	Contains the jumpshort instruction (1 byte), the offset of the bootstrap code (1 byte), and a NOP.
03	8	OEM name	The name of the OS that formatted the partition. Can be used to determine legacy OS presence.
0B	2	# of bytes per sector	The total number of bytes each sector holds.
0D	1	# of sectors per cluster	The total number of sectors each cluster holds.
0D	2	# of reserved sectors	The number of reserved for sectors the boot record.
10	1	# of FATs	The total number of File Allocation Tables. This is usually 2 (one primary plus one backup).
11	2	Root entries	The maximum number of entries possible in the root entry. Sets the number of subdirectories off root that are allowed.
13	2	Total sectors	Total number of sectors. Used for partitions smaller than 32MB and floppy drives .
15	1	Media type	F0 for a floppy drive, F8 for a hard drive.
16	2	# of sectors per FAT	Total number of sectors in each FAT. Used for FAT12/16.
18	2	# of sectors per track	Total number of sectors in each track.
1A	2	# of heads per cylinder	Total number of drive heads.
1C	4	# of hidden sectors	The number of sectors in the MBR until the boot record begins.
20	4	Total sectors	The total number of sectors in the partition. Used for partitions larger than 32MB.
24	4	# of sectors per FAT	Total number of sectors in each FAT. Used for FAT32.
28	2	Flags	Reserved for determining FAT mirroring status. Allows for the use of the backup FAT as the primary on FAT32 systems.
2A	2	Version	The file system version number.
2C	4	Root cluster	The cluster number where the root cluster begins.
30	2	Info sector	The sector number of the file system information sector.
32	2	Boot backup location	The sector number of the boot area backup location on the drive (if present).
34	12	Reserved	Reserved for future use.
40	1	Drive Id	00 for a floppy disk, 80 for a hard disk.
41	1	NT reserved	Set to 00 by NT when the drive is formatted.
42	1	Extended boot signature	Set to 29 to indicate the presence of the serial number, partition name, and FAT type are present.
43	4	Volume serial number	A unique number assigned to a partition at format time. Both Quick and Full formats reassign a serial number.
47	11	Volume/partition name	An 11-character name assigned to the volume by the person formatting the drive.
52	8	FAT type	FAT12, FAT16, or FAT32. This is used by some utilities, but not the OS itself.
5A	420	Executable bootstrap	Starts the first file to boot the system itself.
01 FE	2	Executable signature	Added as 55 AA when formatted. Otherwise, the operating system will not be registered by the BIOS as present.