Understanding Internet Addresses

By Walton Dell
1/11/97

Technical stuff:

Every computer on the Internet has a number called an IP address. This number is equally divided into four parts (ranging from 0 to 255) and separated with dots. An IP address looks like this: 123.123.123.123 This number can be thought of as Earth coordinates for that computer (simplified). There are more than 2 billion possible combinations.

When your computer connects with your Internet Service Provider, their computer gives your computer a temporary number for that connection (then the next person to connect gets it).

Computers may like numbers, but people like names. This is why most computers also have a name. When your computer connects to your ISP, it is also connecting to a computer that keeps a database of all known computer names and the corresponding numbers. This computer is called a Dynamic Name Server (DNS) computer. When your computer wants to communicate with a computer named www.yahoo.com, it first asks the DNS computer for the correct number; Then your computer uses the number to contact the yahoo computer.

The essential stuff:

Computer names are divided into different parts, each separated by a dot. The first part of a computer name commonly designates its function. Not all computers are named like this, but many are. Here are the most common computer types:

www.	World Wide Web -- When you view web pages, you are using www computers. (These are very common.)
news.	Newsgroup -- These computers hold discussion forums (newsgroups). Your ISP should provide this service.
mail.	E-mail -- These computers handle email. Sometimes 'mail.' is left out of the name, or it may be 'pop.' or 'pop3.' for the computer that receives email and 'smtp.' for the computer that sends email.
ftp.	File transfer -- For downloading & uploading files; similar to www computers.
irc.	Internet Relay Chat -- These computers handle real-time chat.

The next part of the name is the real meat of the thing; it can be anything. Here are some examples:

microsoft, symantec, pepsi, disney

The next part is usually the last part in the United States. It designates the type of place that runs the computer:

.com = commercial .org = organization .net = general network computer (can be commercial) .edu = educational (Universities, Colleges, etc.) .gov = government .mil = military

Finally, non U.S. computers often have a 2 character abbreviation for its country:

.jp = Japan
etc.

Here are some example computer names:

www.disney.com
news.microsoft.com
www.whitehouse.gov
www.pbs.org

This is all the address you need if you want to view the home page for a www computer. A web browser (such as Netscape) will have a place to type in an address. For many web sites, you do not even have to type the www. You can get to Yahoo by simply typing yahoo.com. If you type in wdell.com, you will access the home page for my web site. However, if you want to access a particular file on a computer, you need to specify the folder, (and subfolders), and filename for the file that you want. This is very similar to the way PC files are specified. Here are some examples on my web site:

wdell.com
[computer] [no file specified, loads default home page]

wdell.com/sample.html
[computer] [file named "sample", which is an "html" file (a web page file)]

wdell.com/sm64
[the wdell.com computer] [the sm64 folder] [no file specified, so the default page for the sm64 folder is loaded]

Email addresses are very different from web addresses. You do not include www, and you put the user name of the person you are emailing in front of the computer's name with an at sign (@) between. For example:

(username)@(computer)
joe@microsoft.com 
president@whitehouse.gov