Your Internet Consultant - The FAQs of Life Online

3.3. What is a domain name?

Computers are computers and people are people, and the two species work in very different ways. Computers like to work with lots of numbers, but people generally prefer words and names to numbers. (That's why I'm more likely to walk up you a friend on the street and say, "Hi, Jim!" than call him by, say, his social security number.)

Every host on the Internet has an address: a series of four numbers, each less than 256, separated by periods. Although the computers are perfectly happy with this arrangement ("Hello, 137.50.188.22, I have some mail for you from a user at 137.150.10.10."), humans are less than content blurting those numeric addresses. So, for the convenience of us humans, computers on the Net also have names.

Each computer's address--formally called its internet protocol (IP) address, is made of four numbers separated by dots, like these:

You can generally refer to a computer by its name or its address. For instance, you can type ftp archie.au or you can type ftp 139.130.4.6. You should connect to the same machine either way. Electronic mail is an exception, using only system names, not addresses. E-mail addresses look like savetz@rahul.net, never like savetz@192.160.13.1.

Here's an example: one computer at Humboldt State University (my alma matter) is called 

turing.cnrs.humboldt.edu
In this example, there are four words separated by periods. The computer's name (or hostname) is turing. cnrs.humboldt.edu is the domain of this machine. (And each word of the domain is called a subdomain.)

The domains provide information about the computer, from most specific information (on the left) to least specific information (on the right). turing.cnrs.humboldt.edu is the fully qualified domain name of the host, a computer with its own IP address. That computer--and its name--is maintained by the College of Natural Resources and Sciences (a.k.a. cnrs) department at Humboldt State University. Humboldt is part of a national group (edu) that lumps together all educational institutions. So, by carefully reading the computer's name (and decoding some acronyms), we can learn quite a lot about an Internet site.

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