all system functions are invoked via win32 APIs.
If you don't want to tangle with them directly, i suppose you can try to
find someone who created a managed wrapper for those APIs.
Either way though, the code will be using P/invoke as file mapping is
completely done in unmanaged code. Also, to take full advantage of it,
you'll likely be using unsafe code blocks as well.
-Rob Teixeira [MVP]