Beyond the Basics: What Really Happens at the System Level When You Open a URL

A technical deep-dive published on DEV Community breaks down the full low-level sequence triggered when a user types a URL like google.com and presses Enter. The process begins with a hardware interrupt from the keyboard, which the OS kernel handles before passing the input to the browser's UI thread. The browser then checks HSTS settings, resolves the domain through a multi-tiered DNS hierarchy spanning browser cache, OS cache, and recursive resolvers, before obtaining an IP address. Once the IP is known, the OS opens a network socket and uses the Address Resolution Protocol to map the IP to a physical MAC address on the local network. The article argues that while most developers cite DNS lookup and HTTP requests in interviews, the actual process involves dozens of low-level protocols completing a complex sequence in under 100 milliseconds.