Numbers are, of course, easy for the computer to deal with, but confusing for human users. Computer scientists developed a system called the Domain Name Server (DNS) system. It was devised to give verbal equivalents to IP numbers. Many computers have domain names in addition to IP addresses. The Domain names are paired with the IP numbers in a large database that is distributed throughout the Internet. So far, you may not have used any IP numbers. Most of the computers you access through a web browser have a domain name. You will only need to know about IP numbers when you encounter a computer which does not have a name assigned.
The DNS system is organized in a tree - like structure based loosely on the organization of the ARPANet. All the computers in the Internet are thought of as belonging to a specific wide domain. Each domain might have a number of subdomains, which might have a number of computers in it. Finally, each computer may have a number of users who own or regularly use the computer.
Part of the DNS tree structure is shown here:
There are two main ways of organizing the highest level domains. The ARPANet defined domains with three character abbreviations based on the type of organization which owns the computers. The most common of these names is summarized in the table below:
| Domain | Type of Organization |
| .edu | Educational institution |
| .com | Commercial or business |
| .gov | Government organization |
| .org | Non-profit organization |
You might also find two character domain abbreviations, like .fr or .au. These are international domains, which represent the country of the computer. .fr stands for France, and .au stands for Australia.