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Format of DOS 3.30 drive data table

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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 13 - N
1 - B 14 - O
2 - C 15 - P
3 - D 16 - Q
4 - E 17 - R
5 - F 18 - S
6 - G 19 - T
7 - H 20 - U
8 - I 21 - V
9 - J 22 - W
10 - K 23 - X
11 - L 24 - Y
12 - M 25 - Z

06h

19 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

0Ah

BYTE

media descriptor, 00h if unknown

0Bh

WORD

sectors per FAT

0Dh

WORD

sectors per track

0Fh

WORD

number of heads

11h

WORD

number of hidden sectors

19h

BYTE

flags
bit 6 : 16-bit FAT instead of 12-bit FAT

1Ah

WORD

number of DEVICE OPEN calls without corresponding DEVICE CLOSE

1Ch

11 BYTEs

volume label or "NO NAME " if none (always "NO NAME" for fixed media)

27h

BYTE

terminating null for volume label???

28h

BYTE

device type (see #01561 at INT 21/AX=440Dh"DOS 3.2+")

29h

WORD

bit flags describing drive (see #02604)

2Bh

WORD

number of cylinders

2Dh

19 BYTEs

BIOS Parameter Block for highest capacity supported

40h

3 BYTEs

???

43h

9 BYTEs

filesystem type???, default = "NO NAME " (apparently only MS-DOS 3.30 fixed media, nulls for removable media and PC-DOS 3.30)

4Ch

BYTE

least-significant byte of last-accessed cylinder number

---removable media---

4Dh

DWORD

time of last access in clock ticks (FFFFFFFFh if never)

---fixed media---

4Dh

WORD

partition
FFFFh = primary
0001h = extended

4Fh

WORD

absolute cylinder number of partition's start on physical drive (always FFFFh if primary partition)

See Also:

#02602,#02603