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Copyright 1991 David Jurgens |
Disk Partition Table (Fixed disk boot record)
Offset Represents: (see format below)
01BE Partition 1 data table (16 bytes)
01CE Partition 2 data table (16 bytes)
01DE Partition 3 data table (16 bytes)
01EE Partition 4 data table (16 bytes)
01FE Signature (hex 55 AA, 2 bytes)
Offset from beginning of partition data shown above:
Offset Size Description
00 byte boot indicator
01 byte beginning sector head number
02 byte beginning sector (2 high bits of cylinder #)
03 byte beginning cylinder# (low order bits of cylinder #)
04 byte system indicator
05 byte ending sector head number
06 byte ending sector (2 high bits of cylinder #)
07 byte ending cylinder# (low order bits of cylinder #)
08 dword number of sectors preceding the partition
0B dword number of sectors in the partition
Boot indicator (BYTE)
00 - non-bootable partition
80 - bootable partition (one partition only)
System Indicator (BYTE)
00 - unknown operating system
01 - DOS with 12 bit FAT, 16 bit sector number
02 - XENIX
04 - DOS with 16 bit FAT, 16 bit sector number
05 - DOS Extended partition (DOS 3.3+)
06 - DOS 4.0 (Compaq 3.31), 32 bit sector number
51 - Ontrack extended partition
64 - Novell
75 - PCIX
DB - CP/M
FF - BBT
Signature
Hex 55AA marks the end of valid boot sector. This is also
required in each of the partition boot records.
Sector/Cylinder
2 bytes are combined to a word similar to INT 13:
│7│6│5│4│3│2│1│0│ 1st byte (sector)
│ │ └─┴─┴─┴─┴─┴── Sector offset within cylinder
└─┴───────────── High order bits of cylinder #
│7│6│5│4│3│2│1│0│ 2nd byte (cylinder)
└─┴─┴─┴─┴─┴─┴───── Low order bits of cylinder #
- all partitions begin on sector 1 head 0, except the first
partition which follows the disk's master boot record and begins
in sector 2
- some of this information may vary with some variants of DOS 3.2
and DOS 3.3 that use their own sectoring scheme for large disks
- see INT 21,32 Disk Partition Table
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