You also have to know about how computers work, how they represent numbers, how and where they store memory, how computers process information, you have to know

You also have to know about how computers work, how they represent numbers, how and where they store memory, how computers process information, you have to know about interrupts low level os stuff, networking protocols, physical hardware limitations, debugging low level byzantine failures. You have to know a lot more than just C syntax. I haven't even mentioned computer science, best practices, working with others, architecture and UI topics.