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Format of COMPAQ DOS 3.31 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

25 BYTEs

BIOS Parameter Block (see #02603)

1Fh

6 BYTEs

reserved fields from BPB above???

25h

BYTE

flags
bit 6 : 16-bit FAT instead of 12-bit FAT
bit 5 : large volume???

26h

WORD

device-open count???

28h

11 BYTEs

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

33h

BYTE

terminating null for volume label

34h

BYTE

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

35h

WORD

bit flags describing drive (see #02604)

37h

WORD

number of cylinders

39h

25 BYTEs

BIOS parameter block for highest capacity drive supports

52h

6 BYTEs

??? apparently always zeros

58h

BYTE

least-significant byte of last-accessed cylinder number

---removable media---

59h

DWORD

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

---fixed media---

59h

WORD

partition
FFFFh = primary
0001h = extended

5Bh

WORD

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

See Also:

#02601,#02603