Format of DOS 4.0-7.0 drive data table:
Offset Size Description )
00h DWORD pointer to next table (offset FFFFh if last table)
04h BYTE physical unit number (for INT 13)
05h BYTE logical drive number (0=A:)
06h 25 BYTEs BIOS Parameter Block (see also INT 21/AH=53h)
Offset Size Description
00h WORD bytes per sector
02h BYTE sectors per cluster, FFh if unknown
03h WORD number of reserved sectors
05h BYTE number of FATs
06h WORD number of root dir entries
08h WORD total sectors (refer to offset 15h if zero)
0Ah BYTE media descriptor, 00h if unknown
0Bh WORD sectors per FAT
0Dh WORD sectors per track
0Fh WORD number of heads
11h DWORD number of hidden sectors
15h DWORD total sectors if WORD at 08h is zero
1Fh BYTE flags
bit 6: 16-bit FAT instead of 12-bit
bit 7: unsupportable disk (all accesses will return Not Ready)
20h WORD device-open count
22h BYTE device type (see #01561 at INT 21/AX=440Dh"DOS 3.2+")
23h WORD bit flags describing drive (see #02604)
25h WORD number of cylinders (for partition only, if hard disk)
27h 25 BYTEs BIOS Parameter Block for default (highest) capacity supported
40h 6 BYTEs reserved (part of BPB above)
46h BYTE last track accessed
---removable media---
47h DWORD time of last access in clock ticks (FFFFFFFFh if never)
---fixed media---
47h WORD partition (FFFFh = primary, 0001h = extended)
always 0001h for DOS 5+
49h WORD absolute cylinder number of partition's start on physical drive
(FFFFh if primary partition in DOS 4.x)
------
4Bh 11 BYTEs volume label or "NO NAME " if none (apparently taken from
extended boot record rather than root directory)
56h BYTE terminating null for volume label
57h DWORD serial number
5Bh 8 BYTEs filesystem type ("FAT12 " or "FAT16 ")
63h BYTE terminating null for filesystem type
SeeAlso: #02601,#02602