What operating systems are written in the C language?

Answer 1

They're not.

Perhaps since the advent of UNIX, it has become obvious that writing software in higher level languages makes for less debugging and more reliable code, but originally OSs were written in the assembler of the machine they ran on.

Believe it or not, most OS geeks think of "C" as a high level language. The fact that you can directly address all of memory and that it has a concept of interupt handling makes it an ideal candidate for portable OS code (consider that UNIX and later Linux now runs on virtually all hardware platforms).

Java specifically prevents you from directly accessing random memory. You can only address memory that Java has allocated to you in the form of objects. You can imagine writing a function that allowed java to directly access that memory ... but what would that function be written in? Probably C.

In fact, even version of the java engine I have seen was written in C or C++.

Way back when, the majority of programmers out there had experience with assemblers and C was such an advance that there was no reason to turn back.

By the way, the vast majority of OSs written in C still have a tiny bit of assembler associated with them associated with page handling and interupts.

In short C is the highest low level language, where you define "low level language" as one that can directly access memory by address instead of as an object. Alternately, you can say that C is high level language that has the advantage of being able to directly access memory by ... etc.

Problem is - the ability to talk about addresses instead of object handles makes it very easy to write bad code. And there is a LOT of bad C out there.