Why can I not create files/folders with these names?

Question

Can anyone provides me details of why Windows does nto allow to create file/folders with below names?

• PRN
• AUX
• NUL
• LPT1
• COM1
• Potential drive letter - A: to Z:
• Other characters (such as <(less than), >(greater than), :(colon), "(double quote), /(forward slash), \(backslash), |(vertical bar or pipe), ?(question mark), *(asterisk)

Answer 1

Full details of what is allowed from MSDN:

http://msdn.microsoft.com/en-us/library/aa365247(VS.85).aspx

• Use a period to separate the base file name from the extension in the name of a directory or file.

• Use a backslash () to separate the components of a path. The backslash divides the file name from the path to it, and one directory name from another directory name in a path. You cannot use a backslash in the name for the actual file or directory because it is a reserved character that separates the names into components.

• Use a backslash as required as part of volume names, for example, the "C:\" in "C:\path\file" or the "\server\share" in "\server\share\path\file" for Universal Naming Convention (UNC) names. For more information about UNC names, see the Maximum Path Length Limitation section.

• Do not assume case sensitivity. For example, consider the names OSCAR, Oscar, and oscar to be the same, even though some file systems (such as a POSIX-compliant file system) may consider them as different. Note that NTFS supports POSIX semantics for case sensitivity but this is not the default behavior. For more information, see CreateFile.

• Volume designators (drive letters) are similarly case-insensitive. For example, "D:\" and "d:\" refer to the same volume.

• Use any character in the current code page for a name, including Unicode characters and characters in the extended character set (128–255), except for the following:

  • The following reserved characters:

    • < (less than)
    • > (greater than)
    • : (colon)
    • " (double quote)
    • / (forward slash)
    • \ (backslash)
    • | (vertical bar or pipe)
    • ? (question mark)
    • * (asterisk)

  • Integer value zero, sometimes referred to as the ASCII NUL character.

  • Characters whose integer representations are in the range from 1 through 31, except for alternate streams where these characters are allowed. For more information about file streams, see File Streams.

  • Any other character that the target file system does not allow.

• Use a period as a directory component in a path to represent the current directory, for example ".\temp.txt". For more information, see Paths.

• Use two consecutive periods (..) as a directory component in a path to represent the parent of the current directory, for example "..\temp.txt". For more information, see Paths.

• Do not use the following reserved device names for the name of a file:

  CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9. Also avoid these names followed immediately by an extension; for example, NUL.txt is not recommended. For more information, see Namespaces.

• Do not end a file or directory name with a space or a period. Although the underlying file system may support such names, the Windows shell and user interface does not. However, it is acceptable to specify a period as the first character of a name. For example, ".temp".

Answer 2

Also, neither a space nor a period can be used at the end of a name. Further, files cannot have the following reserved device names: 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 the case does not matter in Windows.

There's more information you may find useful on the page that came from (Source).