Getting to the Root of All E-Mail (washingtonpost.com)

And tucked away in a less-traveled back corner of one of the server rooms, behind the door of a black tower that looks no different than any of the others, is the principal reason for all the precautions: the A root server.

Most people envision the Internet as a global network that resides on no single physical system or network of systems. While that picture is roughly correct, key pieces of the Internet's technological backbone are concentrated in a handful of physical locations around the world.

The Domain Name System (DNS) makes the Web easy to navigate by translating long Internet protocol (IP) numbers into memorable Web and e-mail addresses. It relies on a hierarchy of physical root servers to inform computers connected to the Internet where they need to look to find specific locations online.

At the top of that hierarchy is the A root server, which every 12 hours generates a "zone" file, which in turn tells a dozen other root servers spread around the world what Internet domains exist and where they can be found.