DOS reserves some device names for its own use.  You should not use them as
filenames.  Their names and meanings are described below:

CON  - This specifies the console screen and keyboard.  If it is used as
       an input device, pressing the Ctrl-Z key will generate an "end-of-file"
       indication and end the use of CON as an input device.

PRN or LPT1  - This specifies the first parallel printer.  The printer device
               may be used as an output device only.

AUX or COM1  - This is the first Asynchronous Communications Adapter port.

NUL  - This is a nonexistent device that can be used when testing programs
       or where only certain portions of the output should be displayed or
       printed.  As an input device, an "end-of-file" is generated on the
       first read, as a high speed output device the write operation is
       simulated, but no output is generated.

LPT2  - The second parallel printer (for output only).

LPT3  - The third parallel printer (for output only).

COM2  - The second Asynchronous Communications Adapter port.
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