So that people don’t have to remember strings of numbers, host computers also have
names. The name of each host computer consists of a series of words separated by dots.
The last part of the domain name is called the top-level domain (TLD) and indicate the type of organization that owns the domain. The original seven three-letter TLDs are the following:
com -- Originally for commercial organizations, but now used by
individuals, government agencies, and nonprofits as well
net -- Internet service providers and other network-related companies
org -- Noncommercial (often nonprofit) organizations
gov -- government agencies
mil -- military
edu -- Educational domains
int -- International organizations like NATO and the International Red Cross
More three-or-more-letter TLDs are coming into use, such as these:
aero -- Airlines
arpa -- Internet infrastructure (named after the U.S. government agency that
originally created the Internet)
biz -- Businesses
coop -- Cooperatives
info -- Anyone
museum -- Museum
name -- Individuals
Two-letter TLDs indicate the country in which the organization that owns the
computer is located. U.S. organizations can register domains that end with us. Canadian
organizations, for instance, usually have the TLD ca.
The last two parts of a host computer name constitute the domain. The second-to-last
part of the name (the second-level domain) is chosen by the organization that owns the
computer and is usually some variant of the organization’s name. e.g Computers at the McGraw-Hill publishing company are named
with the domain mcgraw-hill.com.
Because most organizations own more than one computer on the Internet, most
host computer names have at least one more part, preceding the domain name and
called a third-level domain (or sometimes a subdomain). This additional part (or parts)
is assigned by the organization itself. e.g mail.yahoo.com, www.yahoo.com
One host computer can have many different names. For example, many ISPs also
offer domain hosting, which means that they allow your domain name to be applied to
one of their host computers. Domain hosting enables you to have your own domain
name, even if you don’t have a host computer.
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