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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.
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    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.

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       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.