en:docs:dos:api:int21:1c

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

2018/09/07 07:04 · prokushev

Int 21H, AH=1CH

Version

1 and higher

Brief

GET ALLOCATION INFORMATION FOR SPECIFIC DRIVE

Family API

none

Input

      AH = 1Ch
      DL = drive (00h = default, 01h = A:, etc)

Return

AL = sectors per cluster (allocation unit), or FFh if invalid drive

      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
      on a DBLSPACE drive, the total number of clusters is based on the
        estimated compression ratio
      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=1Bh,AH=36h

Note


en/docs/dos/api/int21/1c.txt · Last modified: 2020/12/08 09:46 by prokushev