alex/what-happens-when

"What happens when you type google.com into your browser and press Enter?" is one of the most famous interview questions in software engineering because it touches almost every layer of a computer system. This repository is a community-maintained, exhaustive written answer to exactly that question. The document traces the full journey of a single browser request from the physical keystroke that triggers the keyboard hardware interrupt, through the operating system's key event handling, the browser parsing the URL, DNS resolution, TCP connection establishment with the three-way handshake, TLS negotiation, the HTTP request and response, HTML parsing, CSS and JavaScript evaluation, page rendering, and all the way to pixels appearing on screen. Each step is covered in technical depth, referencing the actual protocols, system calls, and hardware mechanisms involved. This is a learning resource, not executable software. You would read it when preparing for technical interviews at companies that ask systems knowledge questions, when you want a structured tour of how the modern web stack actually works end to end, or when you have a gap in your mental model of any particular layer and want a detailed reference to fill it in. The repository is maintained as a plain text file and accepts community contributions that add more depth or correct inaccuracies. It has no programming language and no runnable code, only written technical explanation. It is one of the most widely referenced resources in the software engineering community for understanding full-stack networking and systems fundamentals.