Function 44h (68)        I/O Control for Devices (IOCTL)             Overview

Passes information to a device (or file) or gets information from a
device (or file).

On entry:      AH         44h
AL         Subfunction
BX         File handle
or   BL         Drive number (0=default, 1=A, etc.)
CX         Number of bytes to read or write
DS:DX      Data or buffer

Returns:       See entries for each subfunction.

Network:       Subfunctions 00h and 08h are not supported.
                                                                          

Function 44h (IOCTL) offers a number of subfunctions (16 in DOS 3.3,
10 in DOS 3.0, 8 in DOS 2), all having to do with the exchange of
information between an application and a device (or file). Only
subfunctions 00h, 06h, and 07h are defined for files. In all cases,
the subfunction to be performed is determined by the value in AL, as
follows:

  AL           Subfunction
00h          Get device information  (returned in DX)
01h          Set device information  (from DX; DH must be 0)
02h          Read bytes from the device control chanel into memory at
DS:DX  (character device)
03h          Write bytes from memory at DS:DX to the device control
channel  (character device)
04h          Read bytes from from the device control chanel into
memory at DS:DX  (block device)
05h          Write bytes from memory at DS:DX to the device control
channel  (block device)
06h          Get input status
07h          Get output status
08h          Is block device removable?  (DOS 3.0 and later)
09h          Is logical device local or remote  (DOS 3.1 and later)
0Ah          Is handle local or remote? (DOS 3.1 and later)
0Bh          Change sharing retry count (DOS 3.0 and later)
0Dh          Generic IOCTL request for block devices (DOS 3.2)
0Eh          Get Logical drive  (DOS 3.2 and later)
0Fh          Set logical drive letter (DOS 3.2 and later)

See the separate entries for specific information about each
subfunction.

                                                                          

Notes:         Only functions 00h, 06h, and 07h are defined for
files.

Subfunctions 00h and 08h are not supported on
network devices.  Subfunction 0Bh requires file
sharing, which is loaded with the SHARE command.


44h (68) I/O Control for Devices (IOCTL) Overview