In previous versions of .NET we could check whether process is 64-bit or not. It is not obvious solution - we check length of pointers.
With .NET 4.0 there are two new properties in Environment class. Is64BitProcess returns true if we are currently running in 32-bit mode. It is equivalent to our old-style check of IntPtr.Size == 4.
Is64BitOperatingSystem is something completely new. It will return true if operating system is capable of running 64-bit programs. This opens possibility of detecting 64-bit environment even if we run in 32-bits ourself. It will not be used often but it is good thing to have when e.g. running other processes.