Some call it a bug. Others see it as a small sacrifice in the name of backward compatibility. The point is that no one is entirely sure why they still exist, but if you don't already know, there is a series of reserved names you cannot use in your files. For example: Open Notepad in Windows 10, type something, and try to save the file as 'aux.txt'. Surprised by the error? To understand its origins, we need to travel back to the mid-1970s. Pre-DOS, pre-Space Invaders, pre-Atari 2600.
Reserved Names and the Windows 'Error'
In 1974, Gary Kildall created the CP/M operating system, which became the de facto standard in the computer industry. CP/M was fairly robust but also carried some important limitations, including the 8.3 filename format (eight characters, a dot, three-letter extension, that's it) and the absence of directories. At the same time, the commands that controlled devices under the PIP (Peripheral Interchange Program) tool were crude but effective. Want to print something? The command is PRN:. CON: represented the console. AUX: was an auxiliary device, but in the initial versions of CP/M, PUN: (paper tape punch) and RDR: (paper tape reader) were used. Over the years, CP/M gave way to developments like QDOS/86-DOS, which in turn served as the basis for PC-DOS/MS-DOS. One of the priorities in these new operating systems was to maintain a certain degree of backward compatibility with CP/M, and thus they inherited several of its features, whether freely accessible to the user or reserved for internal use.
44 years later, a Twitter user named @Foone rediscovered those reserved names we cannot use. Want to create a file named NUL? You can't. A folder named CON? You can't either. Naturally, this is not exclusive to Windows 10. Many of our readers might remember the famous c:/con/con error that crashed Windows 9x. The full list of reserved names (according to Microsoft and its official documentation) is CON, PRN, AUX, NUL, COM1 through COM9, and LPT1 through LPT9. The first four are the most 'classic', so to speak. COM names refer to serial ports, and LPT names to parallel ports.
Now... 'reserved' doesn't mean 'impossible'. With the correct command, any user can create files and folders using historically forbidden names. The image we shared above presents the example of a folder named CON. If you try to create it with just 'md', Windows will throw an invalid directory name error, but adding \\.\ to the full path will make the command work. However, its use is not recommended. Be careful if you decide to store anything there.
Source: threadreaderapp.com
