A runtime is the environment in which a program executes, providing the core services and behaviors that the code relies on. It manages tasks such as memory allocation, garbage collection, type checking, and interfacing with the operating system. Different programming languages have different runtimes that implement their execution models. For example, Python, Node.js, and Java each include runtimes that load code, execute instructions, and manage resources. The runtime determines how programs handle errors, scheduling, async operations, and external libraries. Understanding a language’s runtime is essential for writing efficient, predictable code.
how it works
When a program starts, the runtime loads the necessary libraries and initializes internal structures. It then reads code, executes functions, and manages interaction with the operating system. Some runtimes include virtual machines that interpret bytecode or just in time compile it into machine code. Others rely on native binaries compiled ahead of time. Runtimes often include event loops, garbage collectors, and system call wrappers. Backend systems depend on runtimes to manage long lived processes and handle concurrent tasks. Understanding runtime behavior helps developers reason about performance, memory usage, and debugging.