Как проверить разрядность системы?

Начиная с 4 версии фреймворка существует простой способ проверить разрядность ОС, используя статический класс Environment и его свойство Is64BitOperatingSystem:

using System;
static string GetOSBit()
{
    if (Environment.Is64BitOperatingSystem)
        return "x64";
    else
        return "x32";
}

Console.WriteLine(GetOSBit());

Решил проблему так:

internal class OSCheckBit
{
    private static bool Is32BitProcessOn64BitProcessor()
    {
        IsWow64ProcessDelegate fnDelegate = GetIsWow64ProcessDelegate();
        if (fnDelegate == null)
            return false;
        bool isWow64;
        bool retVal = fnDelegate.Invoke(Process.GetCurrentProcess().Handle, out isWow64);
        if (retVal == false)
            return false;
        return isWow64;
    }
    private static IsWow64ProcessDelegate GetIsWow64ProcessDelegate()
    {
        IntPtr handle = LoadLibrary("kernel32");
        if (handle != IntPtr.Zero)
        {
            IntPtr fnPtr = GetProcAddress(handle, "IsWow64Process");
            if (fnPtr != IntPtr.Zero)
                return (IsWow64ProcessDelegate)Marshal.GetDelegateForFunctionPointer((IntPtr)fnPtr, typeof(IsWow64ProcessDelegate));
        }
        return null;
    }
    public enum SoftwareArchitecture
    {
        Unknown = 0,
        x32 = 1,
        x64 = 2
    }
    static public SoftwareArchitecture OSBits
    {
        get
        {
            SoftwareArchitecture osbits = SoftwareArchitecture.Unknown;
            switch (IntPtr.Size * 8)
            {
                case 64: osbits = SoftwareArchitecture.x64; break;
                case 32: if (Is32BitProcessOn64BitProcessor())
                             osbits = SoftwareArchitecture.x64;
                    else
                        osbits = SoftwareArchitecture.x32;
                    break;
                default:
                    osbits = SoftwareArchitecture.Unknown;
                    break;
            }
            return osbits;
        }
    }
    [DllImport("kernel32", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
    public extern static IntPtr LoadLibrary(string libraryName);
    [DllImport("kernel32", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
    public extern static IntPtr GetProcAddress(IntPtr hwnd, string procedureName);
    private delegate bool IsWow64ProcessDelegate([In] IntPtr handle, [Out] out bool isWow64Process);

Вызов: Console.WriteLine($"Версия Вашей ОС: {OSCheckBit.OSBits}");