So, what does "URL" mean? Depending on who you talk to, it's an abbreviation for either Uniform Resource Locator or Universal Resource Locator. Both are equally correct. But what is it?

The URL is a code string that indicates both the exact location of a particular document or destination on the Internet and the data transmission method (the "Transport Protocol," which is just a "language" that computers use to communicate with one another) that should be used to retrieve the information.

Every URL has two major parts: the Header and the Address. Let's take a look at the URL for a particular page on the TMLP Website (the one we're on right now, in fact):

http://www.tmlp.com/tutorial/coursep3.htm

The portion of the URL above shown in red is the Header. The portion of the URL above shown in blue is the Address.

Let's take a look at each piece individually. We'll start with the Header.

http : //

The Header itself is broken into three separate pieces.

The portion shown in purple above (in this case, "http") is called the Transport Protocol. This portion tells the computer viewing a page on the Internet what "language" it should use to retrieve the document. The most common types are:

• HTTP = HyperText Transfer Protocol. These are Web Pages.
  
  
• HTTPS = HyperText Transfer Protocol Secure. These are also Web pages, but all information passed to and from the page is encoded to enhance the security of transactions made using the page. Most often, these pages are used for the purposes of buying things over the Internet via credit cards.
  
  
• FTP = File Transfer Protocol. This is a language used specifically to transfer large files back and forth from location to location.
  
  
• Mailto = Mail To, just like it says. This type of Transport Protocol automatically opens an email program that can be used to send an email to a specfic person.

There are others, but those are the most common.

The colon shown in red above is a separator that indicates the end of the Transport Protocol name.

The two slashes shown in blue above indicate the end of the header and the beginning of a domain name (like www.tmlp.com) These double slashes are only necessary in URL’s that require a domain name in the address.

Now let's take a look at the Address portion.

www.tmlp.com/tutorial/coursep3.htm

The portion of the Address shown above in purple is the Machine Address. Consider this like the file cabinet mentioned above: the address of the actual Web Site.

The portion of the Address shown above in blue is a Directory. Consider this like a particular drawer in the file cabinet.

The portion of the Address shown above in red is the Document. This is the name of the actual Web Page to be displayed.

Most websites also have a particular address called the "Default Document." This is the page that is automatically displayed if no specific document is referenced. For example, the TMLP Online Website has a "Default Document" named "index.htm" When someone on the Internet views

http://www.tmlp.com

the "Default Document" is automatically accessed, thus this is the equivalent of telling the computer on the Internet to view

http://www.tmlp.com/index.html

Let's take a look at a couple more URL's before we move on.

http://www.microsoft.com

What does this URL tell us? The "http" tells us we are looking at a Web page, and the "www.microsoft.com" tells us we're looking at the Microsoft website. There is no document specified, so we know if we open this URL, we'll be looking at the Default Document for the Microsoft website.

ftp://ftp.tmlp.com/win95/arach_full.exe

How about this URL? The "ftp" lets us know that this URL is designed to transfer a file from one place to another. The "ftp.tmlp.com" tells us the file is currently on the TMLP Online FTP site (again, think of it as the file cabinet). The "win95" is a directory, telling us the file is in a directory (or drawer) called "win95." The last part, "arach_full.exe" tells us exactly what file is to be transferred. A computer opening this URL will connect to the TMLP Online FTP server, look in the win95 directory, and download the file "arach_full.exe"

mailto:bobsmith@bobsmith.com

And what about this one? The mailto lets us know that this URL will open up an email program to send an email. You'll notice the double slashes shown in the previous URL's are not included. This is because in this particular case, the URL isn't talking to a particular site, but rather to a particular mail address. Opening this URL would send an email to the address bobsmith@bobsmith.com.

Well, now we know what URL's are. Only problem is, how do we use them? That's where Browsers come in. We'll be getting to them on the next page.