Why do some websites use
www1. rather than
It happens that they've enabled wildcard DNS, and will serve up requests to sub domains named, well anything at all. No, really. Anything at all.
Also... a long time ago, serving up the same content on multiple subdomains named "www#" was a cheap and simple load balancing technique. Each domain would correspond to a physical server. It fell out of common practice with the advent of sane reverse proxies and simplified virtual hosting technologies.