Windows “reserves” certain file names and doesn’t let you use them anywhere. Forget calling a file “con.txt” or “aux.mp3”. This is all because of a choice made in 1974 and Microsoft’s thirst for eternal backwards compatibility.
File Names You Can’t Use
Microsoft provides an official list of reserved file names, and here they are:
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.
You can try it yourself. Try saving a file as “con.txt” or “lpt6.txt” in Notepad. Or try renaming any file to one of these names in File Explorer. Windows just won’t let you do it.
Of course, Windows also restricts file names in other ways. You can’t use various special characters like the following in names, either. Consult Microsoft’s official documentation for more information.
What Happened in 1974, and Why Should We Care?
It is 2018 and this error message is a mistake from 1974.
This limitation, which is still found in the very latest Windows 10, dates back to BEFORE STAR WARS. This bug is as old as Watergate. pic.twitter.com/pPbkZiE57t
— foone (@Foone) November 3, 2018