[United857]

Unless something has changed drastically since when I was at MS, the Windows kernel and the major OS DLLs is pretty much pure C. The GUI/window manager are more C++.

Even Word and Excel were still C (although Office shared much C++ code in a common DLL)

Gotta love legacy code from the 1980s/1990s.

[pjmlp]

When were you there?

Since the new "Going native" wave, C++ has taken the role of main systems programming language, even the DDK now supports it.

Regarding office check their CppCon presentation how the code was ported to C++, refactored and made portable across OS. About 2h session.

[Hydraulix989]

"Going native" meant salvaging Vista's low performance by rewriting everything in C++ that was written in .NET -- .NET was the "wave" here, but it's also the culprit for Vista eating memory like cheap sushi.

[pjmlp]

Yet, the replacement of Win32 API model is with everything being written in the original design of .NET, with AOT native compilation and classes being COM objects.

What killed Vista was politics between OSDev and DevTools units.