CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9
Note that you can’t use these file names with any file extension. So you can’t name a file “con.txt”, “con.jpg”, “or “con.doc”. And Windows isn’t case sensitive, so it doesn’t matter whether it’s CON, con, or CoN—Windows won’t let you use that name.