Naming & Renaming Folders

For the first one, try to create a folder named CON and you will see the following thing happening:

The same thing happens when you try any of the following names:
PRN, LPT1, LPT2, (…), LPT9, NUL, COM1, (…), COM9, and CLOCK$
All of the above names are reserved device names, which cannot be used as file names or folder names, regardless of the file extension. This is a relic from DOS, which has made its way through all versions of Windows, including Windows 7.