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

2018/09/07 07:04 · prokushev

Int 21H, AH=44H, AL=00H


2 and higher



Family API


      AX = 4400h
      BX = handle


CF clear if successful

          DX = device information word (see #01423)
          AX destroyed
      CF set on error
          AX = error code (01h,05h,06h) (see #01680 at AH=59h/BX=0000h)



value in DH corresponds to high byte of device driver's attribute word
        if handle refers to a character device
      Novell NetWare reportedly does not return a drive number in bits 5-0
        for a disk file
      this function was not supported by Digital Research's DOS Plus

Bitfields for device information word: Bit(s) Description (Table 01423) character device

14    device driver can process IOCTL requests (see AX=4402h"DOS 2+")
13    output until busy supported
11    driver supports OPEN/CLOSE calls
 8    ??? (set by MS-DOS 6.2x KEYB)
 7    set (indicates device)
 6    EOF on input
 5    raw (binary) mode
 4    device is special (uses INT 29)
 3    clock device
 2    NUL device
 1    standard output
 0    standard input

disk file

15    file is remote (DOS 3.0+)
14    don't set file date/time on closing (DOS 3.0+)
11    media not removable
 8    (DOS 4 only) generate INT 24 if no disk space on write or read past
        end of file
 7    clear (indicates file)
 6    file has not been written
5-0   drive number (0 = A:)

See also

AX=4401h,INT 2F/AX=122Bh, INT 29


en/docs/dos/api/int21/44/00.txt · Last modified: 2021/04/30 08:43 by prokushev