Online HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens
Boot Sector (since DOS 2.0)
Offset Size Description
00 3bytes jump to executable code
03 8bytes OEM name and version
0B word bytes per sector
0D byte sectors per cluster (allocation unit size)
0E word number of reserved sectors (starting at 0)
10 byte number of FAT's on disk
11 word number of root directory entries (directory size)
13 word number of total sectors (0 if partition > 32Mb)
15 byte media descriptor byte (see MEDIA DESCRIPTOR)
16 word sectors per FAT
18 word sectors per track (DOS 3.0+)
1A word number of heads (DOS 3.0+)
1C word number of hidden sectors (DOS 3.0+)
20 dword (DOS 4+) number of sectors if offset 13 was 0
24 byte (DOS 4+) physical drive number
25 byte (DOS 4+) reserved
26 byte (DOS 4+) signature byte (29h)
27 dword (DOS 4+) volume serial number
2B 11bytes (DOS 4+) volume label
36 8bytes (DOS 4+) reserved
- implementation format not guaranteed in all OEM DOS releases
- BIOS expects a boot sector of 512 bytes
- DOS 3.2 began reading BIOS Parameter Block (BPB) information from
the boot sector, previous versions used only the media byte in FAT
- DOS 4.x added offsets 20-3Dh and offset 20h determines the number
of sectors if offset 13h is zero
- hard disks have a master boot record and partition boot records;
the master boot record and Disk Partition Table (DPT) share the
same sector
[helppc.bosbyte.nl] boot sector