Rust, and virtually every other programming language out there, like C++, D, python, C#, etc. have a runtime library built to aid the programmer. When programming an operating system, you must implement the runtime that the language expects if you wish to use some features of that language. In the case of Rust that would be dynamic heap allocation. The C++ "new" and "delete" operators (analogous to C's malloc() and free() ) are also an example of a runtime that must be implemented for those operators to be used. Python and C# have gigantic runtimes (the interpreter/JIT compiler).