Int 21/AX=4400h

INT 21 - DOS 2+ - IOCTL - GET DEVICE INFORMATION
AX = 4400h
BX = handle

Return:
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)

Notes: 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

See Also: AX=4401h - INT 2F/AX=122Bh


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: INT 29

Category: DOS Kernel - Int 21h - @

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