Function 3Bh            Change Current Directory (CHDIR)

    Changes the current directory to a specified path.

        Entry   AH    = 3Bh
                DS:DX = Pointer to ASCIIZ name of new default directory

        Return  AX = Error code, if CF is set
                     | 03h Path not found

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    Function 3Bh changes the current directory to the directory whose
    path is specified in the ASCIIZ string at address DS:DX; the
    string length is limited to 64 characters.

    The path name may include a drive letter. If a drive other than
    the default drive is specified as part of the new directory path,
    this function changes the current directory on that drive but does
    not change the default drive.