# Asynchronous I/O Models Asynchronous I/O (Input/Output) models allow programs to initiate I/O operations and then continue with other tasks without waiting for the I/O operation to complete. This is particularly useful in systems handling numerous concurrent connections, such as servers. There are various asynchronous I/O models, including: - `Event-driven` or `Reactor` model - `Proactor` model ## Event-driven or Reactor Model In the reactor model, the application registers I/O operations with the reactor, which demultiplexes events and dispatches them to the application when they’re ready. Here's an example in Node.js: ```javascript const fs = require('fs'); fs.readFile('file.txt', (err, data) => { if (err) throw err; console.log(data); }); console.log('Reading file...'); ``` In this example, we're reading a file asynchronously. The `readFile` function doesn't block the rest of the code from executing. While the file is being read, the following `console.log` statement executes. Once the file read operation is complete, the callback function executes. ## Proactor Model In the proactor model, the system's kernel handles the completion of operations. When an operation completes, a completion event is queued, and a user-defined function (the completion handler) is invoked. Here's an example in Python using `asyncio`, a library that implements the proactor model: ```python import asyncio async def main(): with open('file.txt', 'rb') as f: contents = await f.read() print(contents) asyncio.run(main()) ``` In this example, the `main` function opens a file and awaits its contents. While the file is being read, the program can perform other tasks. When the file read operation is complete, the contents are printed to the console. Asynchronous I/O models can significantly improve the efficiency and performance of programs handling numerous concurrent I/O operations.