Agreed. I would say that C teaches you how the OS API works. That doesn't map well to how even a simple computer works, let alone one with multiple processors

Agreed. I would say that C teaches you how the OS API works. That doesn't map well to how even a simple computer works, let alone one with multiple processors, complex memory hierarchies, north and south bridges, various I/O adapters, etc. Don't even get me started on anything virtual or distributed. Knowing C might help, to the extent that code which might be useful to gain such understanding tends to be written in C, but the language itself isn't going to impart those lessons.