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WinAPI Namespaces

WinAPI has two important namespaces:
NT namespaces The lowest level namespace on which other subsystems (such as the Win32 or POSIX subsystem) and other namespaces could be built
Win32 namespaces ?The namespace of the Win32 subsystem?

Win32 namespace

In Winobj.exe (or generally?), the Win32 namespace is found under the folder named Global??.

Prefixes

\\?\ When calling a WinAPI function that accepts a file path, the path can be prefixed with \\?\ which tells the function not to parse the path but to route it directly to the file system.
\\.\ Access the Win32 device namespace instead of the Win32 file namespace (for example to directly access physical disks and volumes, for example \\.\PhysicalDriveN or \\.\CdRomN or \\.\COMN where N is an integer).
File names such as con or aux cannot normally be created. With the \\.\ prefix, it becomes possible. This is demonstrated in the following PowerShell example: 
PS:> mkdir $env:temp/test
PS:> mkdir $env:temp/test/con
mkdir : The directory specified, 'con', is not a subdirectory of…
PS:> mkdir "\\.\$env:temp/test/con"
PS:> new-item "\\.\$env:temp/test/con/aux"
Apparently, the directory cannot be removed in Powershell(?), it's possible in cmd.exe, though: 
C:\> rmdir /s \\.\%temp%\temp\con

Links

MSDN: Naming Files, Paths, and Namespaces.

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