I found this little problem circulating via e-mail and social networks, why we get an error while renaming or creating any file/folder with "con" name. Many posts have wrote that "even Bill Gates or the whole Microsoft Team is unable to explain this". That's not true. Here is the correct explanation.

The actual reason is that Microsoft MS-DOS reserves certain names for system device drivers. If you try to name a file or folder using one of these names, you will receive the error message, "The specified device driver name is not valid." So this is not a bug but a programming constraint. This s applicable to nearly all Microsoft DOS versions.

Below is a list of default device driver names which are not permissible as any file/folder name.

NameFunction
CONKeyboard and display
PRNSystem list device, usually a parallel port
AUXAuxiliary device, usually a serial port
CLOCK$System real-time clock
NULBit-bucket device>
A:-Z:Drive letters
COM1First serial communications port
LPT1First parallel printer port
LPT2Second parallel printer port
LPT3Third parallel printer port
COM2Second serial communications port
COM3Third serial communications port
COM4Fourth serial communications port

I have got the list from DOS prompt. To get it type mem/d|more in the DOS prompt. It will show you the full list of device driver names with address and size.

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