Originally known as the URI – Universal Resource Identifier the term URL has become synonymous with URI and become the most commonly used. It is a string used to describe and identify an Internet resource and how to access it.
Whilst the most common URLs are links to web pages that users will be familiar with and starting with http:// this part of the URL is in fact the part that identifies the protocol being used. A file server might use the File Transfer Protocol and therefore start ftp:// for example.
The next part of a URL describes the actual location of the Internet resource through it’s IP address (or equivalent domain name). For example http://www.yahoo.com would describe the protocol (HTTP) and location required to access the popular search engine and web portal Yahoo!.
Additional information can be specified for example a directory on the server can be specified using the / in this manner: http://www.whateverdomain.com/thedirectory/file.html would identify the protocol, Internet location and directory required to access the file.html resource. Variables can be passed to the server using the ? for example:-
http://www.whateverdomain.com/thedirectory/file.php?type_of_cheese=cheddar would pass the word cheddar to the server as the type_of_cheese variable.
As not all communication will take place on the default port for connection under the protocol (HTTP would usually be port 80 for example) the URL allows this to be specified using a ‘:’ as shown:-
http://www.connecttomeon7676.com:7676 would connect to this domain on port 7676 assuming it allows connections on that port.