You have to study the subject of "reserved words" in windows. All the following are reserved words: The CON is a reserved word for the console
CON, PRN, AUX, CLOCK$, NUL COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9 LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9.
They are used for different things like defining the printer or the communication channels.
see: http://en.wikipedia.org/wiki/Device_file
only after submitting my answer I found that it was answered in http://yedda.com/questions/4952996141581/#postId4956110150171