en:docs:dos:api:int21:1b

Note: This API call is for DOS personality only. Use Family API for portability.

2018/09/07 07:04 · prokushev

Int 21H, AH=1BH

Version

1 and higher

Brief

GET ALLOCATION INFORMATION FOR DEFAULT DRIVE

Family API

none

Input

      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)

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")
        

See also

AH=1Ch,AH=36h

Note

DOS API
Process manager INT 20H, INT 21H: 00H, 25H, 26H, 31H, 34H, 35H, 4CH, INT 22H, INT 27H, INT 28H
File manager INT 25H, INT 26H, INT 21H: 0DH, 0EH, 0FH, 10H, 11H, 12H, 13H, 14H, 15H, 16H, 17H, 19H, 1AH, 1BH, 1CH, 21H, 22H, 23H, 24H, 27H, 28H, 29H, 2EH, 2FH, 32H, 3305H, 36H, 39H, 3AH, 3BH
Character Device I/O INT 29H, INT 21H: 01H, 02H, 03H, 04H, 05H, 06H, 07H, 08H, 09H, 0AH, 0BH, 0AH, 0CH
Signals INT 23H, INT 24H, INT 21H: 3300H, 3301H, 3302H
Memory manager
Date and Time INT 21H: 2AH, 2BH, 2CH, 2DH
Misc INT 21H: 30H, 3306H, 3700H, 3701H, 3702H, 3703H
NLS INT 21H: 3303H, 3304H, 3800H, 3801H
2018/09/04 19:23 · prokushev

en/docs/dos/api/int21/1b.txt · Last modified: 2020/12/08 09:44 by prokushev