Input/Output Errors

    Input/Output (I/O) errors occur when an error is encountered while the
    program is attempting to read data in, write data out, or perform some
    other file operation.

          Hex       Dec       Meaning
          ---       ---       -------
          $01        01       File does not exist
          $02        02       File not open for input
          $03        03       File not open for output
          $04        04       File not open
          $10        16       Error in numeric format
          $20        32       Operation not allowed on a logical device
          $21        33       Not allowed in direct mode
          $22        34       Assign to std files not allowed
          $90       144       Record length mismatch
          $91       145       Seek beyond end-of-file
          $99       153       Unexpected end-of-file
          $F0       240       Disk write error
          $F1       241       Directory is full
          $F2       242       File size overflow
          $F3       243       Too many open files
          $FF       255       File disappeared

    There are two ways of handling these errors. The first way is to let
    the program terminate immediately if an I/O error occurs. This is the
    default method of I/O error handling. This method can be turned on by
    setting the I/O error handling directive to active {$I+}. The error
    code will be printed on the screen in the following format:

           I/O error NN, PC=address
           Program Aborted

    The error code NN is displayed in hexadecimal. The address 'address'
    is also displayed in hexadecimal. If the user is in Turbo Pascal, then
    he is prompted to press the <ESC> key to continue. At that point,
    Turbo Pascal enters the Edit mode and the cursor is placed on the line
    where the I/O error occurred. If the user is not in Turbo Pascal, but
    at the MS-DOS command line, then after the I/O error message is
    displayed, control will return to the operating system. If the user
    wishes to determine the line at which the I/O error occurred, use the
    'Find Run-time Error' option within the Options Menu.

    The second way to handle I/O errors is established by setting the I/O
    error handling directive to passive {$I-}. In this mode, it is up to
    the programmer to handle I/O errors gracefully. If an I/O error does
    occur, then the programmer must call the function IOResult which
    returns the I/O error number. If the programmer does not call
    IOResult, then all further I/O is suspended until IOResult is called.