C# Reading the registry: ProductID returns null in x86 targeted app. "Any CPU" works fine

Question

I have recently moved to a W7 64bit machine with VS 2010. My project is set to run on Any CPU. When I change this to be targeted at x86 I noticed some of my registry calls no longer work.

I am trying to read the ProductID field like so:

RegistryKey windowsNTKey = Registry.LocalMachine.OpenSubKey(@"Software\Microsoft\Windows NT\CurrentVersion");
object productID = windowsNTKey.GetValue("ProductId");

productID is always null when running in x86 mode, when running in "Any CPU" it works correctly. What is going on here?

Answer 1

Some registry keys are redirected by WOW64. More information on this topic is available on MSDN http://msdn.microsoft.com/en-us/library/aa384232(v=vs.85).aspx

If you really want to always access the x64 node (.Net4) :

  RegistryKey localMachine = RegistryKey.OpenBaseKey(Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry64);
  RegistryKey windowsNTKey = localMachine.OpenSubKey(@"Software\Microsoft\Windows NT\CurrentVersion");
  object productID = windowsNTKey.GetValue("ProductId");

Answer 2

This code will get the id for all kinds of os architectures and program architectures. Could be written shorter but I like the readability

    static string GetProductId()
    {
        RegistryKey localMachine = null;
        if (Environment.Is64BitOperatingSystem)
        {
            localMachine = RegistryKey.OpenBaseKey(Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry64);
        }
        else
        {
            localMachine = RegistryKey.OpenBaseKey(Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry32);
        }
        RegistryKey windowsNTKey = localMachine.OpenSubKey(@"Software\Microsoft\Windows NT\CurrentVersion");
        return windowsNTKey.GetValue("ProductId").ToString();
    }