http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx

In the Windows API (with some exceptions discussed in the following paragraphs), the maximum length for a path is MAX_PATH, which is defined as 260 characters. A local path is structured in the following order: drive letter, colon, backslash, components separated by backslashes, and a terminating null character. For example, the maximum path on drive D is "D:\<some 256 character path string><NUL>" where "<NUL>" represents the invisible terminating null character for the current system codepage. (The characters < > are used here for visual clarity and cannot be part of a valid path string.)
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The Windows API has many functions that also have Unicode versions to permit an extended-length path for a maximum total path length of 32,767 characters.
To specify an extended-length path, use the "\\?\" prefix. For example, "\\?\D:\<very long path>". (The characters < > are used here for visual clarity and cannot be part of a valid path string.)