Explores the fundamental differences between stackful coroutines (like Go's goroutines) and stackless coroutines (like Rust's async/await and C++20 coroutines). Explains how stackful coroutines can suspend execution in any nested function by switching stack frames, while stackless coroutines achieve higher performance by avoiding stack frame switches but with limited suspension points. Includes detailed assembly-level explanations of function call stacks, context switching mechanisms, and practical implementation examples in C, Rust, and C++.