pinvoke.net: Edit: Kernel32.GetSystemInfo

@msdn=http://msdn.microsoft.com/en-us/library/windows/desktop/ms724381(v=vs.85).aspx
@pinvoke=http://pinvoke.net/$$$.htm

Summary: Retrieves information about the current system

!!!!C# Signature:
    [DllImport("kernel32.dll", SetLastError=true)]
    internal static extern void GetSystemInfo(ref SYSTEM_INFO Info);
!!!!User-Defined Types:

[StructLayout(LayoutKind.Sequential)]
    internal struct SYSTEM_INFO
    {
        internal ushort wProcessorArchitecture;
        internal ushort wReserved;
        internal uint dwPageSize;
        internal IntPtr lpMinimumApplicationAddress;
        internal IntPtr lpMaximumApplicationAddress;
        internal IntPtr dwActiveProcessorMask;
        internal uint dwNumberOfProcessors;
        internal uint dwProcessorType;
        internal uint dwAllocationGranularity;
        internal ushort wProcessorLevel;
        internal ushort wProcessorRevision;
    }
(from https://referencesource.microsoft.com/#mscorlib/microsoft/win32/win32native.cs,dbd1d00d77377879)

!!!!Alternative Managed API:
To determine whether the OS or Process is x64, using .NET 4, see System.Environment (Is64BitProcess, Is64BitOperatingSystem); http://msdn.microsoft.com/en-us/library/z8te35sa.aspx

Sample Code:
        void Test()
        {
        	NativeMethods.SYSTEM_INFO
        	 info;
        	NativeMethods.GetSystemInfo(out info);
        }
Documentation: GetSystemInfo@msdn on MSDN