In MS-DOS, several special "device files" were available to aid in performing certain tasks, such as clearing the screen or deleting extraneous output from a program. In order to maintain backwards-compatibility, all versions of Winders up to and including Winders Vista will refuse to allow youto create a file with these "reserved" device file names. The followingfile names are reserved: CON, PRN, AUX, NUL, COM1, COM2, COM(all the wya to 9), & LPT1-9
CON, incidentally, was a device file used to capture whatever was printed onscreen.
Now you know, and knowing is half the battle ;)