Int 21/AH=1Bh

DOS 1+ - GET ALLOCATION INFORMATION FOR DEFAULT DRIVE

AH = 1Bh

Return:
AL = sectors per cluster (allocation unit)
CX = bytes per sector
DX = total number of clusters
DS:BX -> media ID byte (see #01356)

Notes: Under DOS 1.x, DS:BX points at an actual copy of the FAT; later versions return a pointer to a copy of the FAT's ID byte. This function may not be properly supported on CD-ROMs and other installable file systems (use AX=4402h"CD-ROM" for CD-ROMs instead)

BUG: DOS 7.10 (Win95B/Win98) reportedly returns incorrect values in AL and DX for FAT12/FAT16 drives, even though it manages correct results for FAT32 drives (DOS windows are not affected, only real-mode DOS)

See Also: AH=1Ch - AH=36h



(Table 01356)
Values for media ID byte:
FFh    floppy, double-sided, 8 sectors per track (320K)
FEh    floppy, single-sided, 8 sectors per track (160K)
FDh    floppy, double-sided, 9 sectors per track (360K)
FCh    floppy, single-sided, 9 sectors per track (180K)
FAh    HP 200LX D:
ROM disk, 16 sectors per track (995K).
HP 200LX E:
(Stacker host drive ???)
F9h    floppy, double-sided, 15 sectors per track (1.2M).
Floppy, double-sided, 9 sectors per track (720K,3.5")
F8h    hard disk
F0h    other media.
(e.g. floppy, double-sized, 18 sectors per track -- 1.44M,3.5")

Category: DOS Kernel - Int 21h - D

Interrups Categories Contents

Shopping
Forum
EMail
Index
Home