Windows "Reserves" some file names and will not let you use them anywhere. Forget about calling a file "con.txt" or "aux.mp3". This is due to a choice made in 1974 and Microsoft's thirst for ever-backward compatibility.
File Name You Can not Use
Microsoft provides an official list of reserved file names, and here they are:
CON, PRN, AUX, ZERO, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9
Please note that you can not use these filenames with any file extension. So you can not name a file "con.txt", "con.jpg", "or" con.doc. "And Windows is not case-sensitive, so it does not matter if it's CON, con, or CoN-Windows lets you do not use that name.
You can try it yourself. Try saving a file like "con.txt" or "lpt6.txt" in the notepad. Or try renaming any file to one of these names in File Explorer Windows will just not let you do it.
Of course, Windows also restricts file names in other ways. You can not use different special characters as follows in the name.
What happened in 1974 and why should we care? 19659009] It's 2018 and this error message is a mistake from 1974.
This limitation, still in the latest Windows 10, returns to STAR WARS. This bug is as old as Watergate. pic.twitter .com / pPbkZiE57t
– foone (@Fone) November 3, 2018  Like @Fone was recently announced on Twitter, this edition will return to 1974. In UNIX, "everything is a file." (The same applies to UNIX-like operating systems like Linux today.) Hardware devices were represented on special paths like / dev / lp0 for the first printer and / dev / tp0 for the console.
1974 put the same term into the CP / M operating system. Unfortunately, CP / M was designed for computers with very little memory and no hard disks. It used multiple discs and no catalogs, so the special files representing devices showed efficiently everywhere on all disks.
So when you saved a text file, you can tell your text editor to "save" it on the printer device, which would print it. But text editors and other applications like adding file extensions such as ".txt", so CP / M just ignored the file extension for these device files. In other words, if a text editor tries to save a file to the name of the printer device followed by ".txt," the CP / M only assumed it was referring to the printer device and ignored the file extension. Now the function worked well in every application-good!
Sure, that's a dirty hack, but who cares? Yes, CP / M is captured. Eventually, PC-DOS came together, and it retained the useful CP / M feature. PC-DOS 2.0 added catalogs back in 1983, but Microsoft chose to have these device files appear in all directories for compatibility with existing DOS software instead of placing them in a special device directory.
Eventually, Windows 95 came together on top of DOS. Windows NT was not based on DOS, but it would be backward compatible with Windows 95 applications. Windows 10 still builds on Windows NT, and it works the same way. The same goes for Windows 7.
Now it's over forty years later and we can still not name files "con.txt" or "aux.mp3" because Windows wants to remain compatible with old applications that can use this feature. This is a good example of how intense Microsoft has undertaken backward compatibility.