Windows 64-bit registry v.s. 32-bit registry

Question

I heard on Windows x64 architecture, in order to support to run both x86 and x64 application, there is two separate/different sets of Windows registry -- one for x86 application to access and the other for x64 application to access? For example, if a COM registers CLSID in the x86 set of registry, then x64 application will never be able to access the COM component by CLSID, because x86/x64 have different sets of registry?

So, my question is whether my understanding of the above sample is correct? I also want to get some more documents to learn this topic, about the two different sets of registry on x64 architecture. (I did some search, but not found any valuable information.)

Answer 1

I ran into this issue not long ago. The short answer is that if you run a 32 bit application on a 64 bit machine then it's registry keys are located under a Wow6432Node.

For example, let's say you have an application that stores its registry information under:

HKEY_LOCAL_MACHINE\SOFTWARE\CompanyX 

If you compile your application as a 64 bit binary and run it on a 64 bit machine then the registry keys are in the location above. However, if you compile your application as a 32 bit binary and run it on a 64 bit machine then your registry information is now located here:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\CompanyX 

This means that if you run both the 32 bit and 64 bit versions of your application on the same machine then they will each be looking at a different set of registry keys.

Answer 2

Your understanding is correct. There wouldn't be any need for a x64 app to access the x86 CLSIDs since it could never load those components anyway and vice versa.

If you want to create component for use by both x86 and x64 then you need to either create a pair of dlls one built for x86 and the other for x64 and register both in their appropriate parts of the registry. The regsrv32.exe in the System32 folder will perversely register the x64 component and the regsrv32.exe in the SysWOW64 folder will register the x86 component.

Alternatively build a .NET assembly for Any CPU which can used by either CPU architecture.