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
- COM0
- COM1
- COM2
- COM3
- COM4
- COM5
- COM6
- COM7
- COM8
- COM9
- LPT0
- LPT1
- LPT2
- LPT3
- LPT4
- LPT5
- LPT6
- LPT7
- LPT8
- LPT9
CON, incidentally, was a device file used to capture whatever was printed onscreen.
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.