Every resource available to remote users over the Internet must have a location identifier referred to as a Uniform Resource Locator (URL). The URL is a naming convention that uniquely identifies the location of a computer, directory, file, or document on the Internet. A basic URL identifies a computer that contains directories, documents, or files. For example, the URL for a Web server at Microsoft looks like this: http://www.microsoft.com.
A URL is composed of several pieces of information. The first part of the URL indicates the TCP/IP-based protocol used to access the remote computer. For Web servers, the URL starts with http:, because hypertext transfer protocol (HTTP) is the protocol used to access Web servers. For FTP servers, the URL starts with ftp:, because FTP is the protocol used to access FTP servers.
The second part of the URL is composed of the DNS host name, enterprise or organization domain name, and an Internet domain name. The second part of the URL looks like this: www.microsoft.com, where www is the host name or host alias,microsoft is the enterprise domain name, and com is the top-level Internet domain name.
A complex URL that connects your computer to a specific document or file has more than these two parts and includes directory and document names. For example, the URL used to connect to an article published for small businesses on the Microsoft Web server looks like this:
http://www.microsoft.com/technet/analpln/smallbiz/sbnisp.htm#What's_an_ISP?2