How is Node.js able to handle many requests without getting bogged down?

Node.js is built on Chrome's V8 JavaScript engine and uses an event-driven, non-blocking I/O model. This architecture makes it lightweight and efficient for I/O-heavy operations.

The core components are: V8 (compiles JavaScript to machine code), libuv (provides the event loop and async I/O), and Node.js bindings that expose OS-level functionality to JavaScript.

While JavaScript runs single-threaded, libuv uses a thread pool (default 4 threads) for operations that can't be done asynchronously at the OS level (file system operations, DNS lookups, some crypto operations). Most network I/O uses the OS's async primitives (epoll, kqueue, IOCP) without needing threads.

The event loop has multiple phases: timers (setTimeout/setInterval callbacks), pending callbacks (I/O callbacks deferred from previous loop), idle/prepare (internal), poll (retrieve new I/O events), check (setImmediate callbacks), and close callbacks.

This architecture excels at: handling many concurrent connections (each doesn't need its own thread), I/O-bound workloads (API servers, real-time applications), and streaming data. It's less suited for CPU-intensive tasks that would block the single JavaScript thread.

For CPU-heavy work, use Worker Threads to run JavaScript in parallel, or offload to separate processes. Understanding this model is key to writing performant Node.js applications.