In the earliest days of the web it was assumed that each web address (www.example.com) would map to a specific physical server with a specific IP address. This server would be named "www" and its principal purpose would be to serve web pages for a single website. And when the Internet was still relatively young, this was a safe assumption. But the web became far more popular than originally expected, and it experienced explosive growth. One thing that became clear during this period of growth was that it is tremendously useful to be able to run more than one website on a single piece of hardware.

Web servers adapted, adding the capability to map a single IP address of a single server to more than one domain name. So, for example, a single piece of server hardware could handle both www.example.com and www.anotherexample.com. Many web hosting providers thrived (and still do) by hosting multiple customers' sites on a single physical server.