Rust is foremost a systems programming language and because the compiler can decide when a variable's lifetime ends, no garbage collection is needed for freeing memory. So when a Rust program executes, it runs in a very lightweight runtime, providing a heap, backtraces, stack guards, unwinding of the call stack when a panic occurs, and dynamic dispatching of methods on trait objects. Also, a small amount of initialization code is run before an executable project's main function starts up.
As we have seen, the standard library gives a lot of functionality. It offers support for various features of its host system: threads, networking, heap allocation, and more. It also links to its C equivalent, which also does some runtime initialization.
But Rust can also run on much more constrained systems that do not need (or do not have) this...
