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 Windows up ...to and including Windows Vista will refuse to allow you to create a file with these "reserved" device file names. The following file names are reserved:
* CON
* PRN
* AUX
* NUL
* COM1
* COM2
* COM3
* COM4
* COM5
* COM6
* COM7
* COM8
* COM9
* LPT1
* LPT2
* LPT3
* LPT4
* LPT5
* LPT6
* LPT7
* LPT8
* LPT9
CON, incidentally, was a device file used to capture whatever was printed onscreen.