Online HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens
DPT/DPB - Drive Parameter Table / Disk Parameter Block
Offset Size Description
00 byte drive (0 = A, 1 = B)
01 byte unit within device, usually equals drive (ramdisk=0)
02 word bytes per sector
04 byte sectors per cluster minus 1
05 byte sectors per cluster (times to shift left or x2)
06 word number of sectors before FAT (boot sectors)
08 byte number of FAT copies
09 word number of root directory entries
0B word number of first data sector
0D word total number of clusters plus 1
0F byte number of sectors used by first FAT
The following fields are DOS version dependant
10 word number of first sector in root directory
12 dword far pointer to current disk device header
16 byte media descriptor byte (see MEDIA DESCRIPTOR)
17 byte zero if disk accessed, (default=FF, must rebuild DPB)
18 dword far pointer to next drive parameter table; offset
is set to FFFFh if last block in chain
1C word current directory cluster number; 0=root
1E 64bytes ASCIIZ current working directory
Fields differing in DOS 3.x
Offset Size Description
1C word starting cluster for free space search
1E 64bytes number of free clusters; FFFFh = unknown
Fields differing in DOS 4.x
Offset Size Description
11 word first sector of root directory
13 dword far pointer to current disk device header
17 byte media descriptor byte (see MEDIA DESCRIPTOR)
18 byte zero if disk accessed, (default=FF, must rebuild DPB)
19 dword pointer to next drive parameter table; offset
is set to FFFFh if last block in chain
1D word starting cluster for free space search
1F word number of free clusters, FFFFh = unknown
- INT 21,32 which is used to read this data resets accessed byte at
offset 17h or 18h (depending on DOS version)
- dword at offset 12h & 13h aren't supported in OS/2 compatability box
- sector references are DOS logical sectors
- see Disk Base Table BPB INT 21,1F INT 21,32
[helppc.bosbyte.nl] drive parameter tbl