2.5.2 Link checking sites
The World Wide Web contains millions of web pages. Many of these pages are impossible to read, even though many existing web pages will reference them: your browser will usually return with some message such as ‘Error 404 Page not Found’ when you try to access them. Error 404 is a standard message returned by web servers when a non-existent page is accessed. It is also the telephone area code for Atlanta in the United States; you will occasionally hear technical staff referring to non-existent web documents as having ‘gone to Atlanta’. There are two main reasons why a web document disappears from the World Wide Web: the first is that the developer or company might have deleted it, for example the company associated with the site has filed for bankruptcy or the individual who developed the site has moved it to another computer. The second reason is that the computer holding the web document is currently malfunctioning or has been switched off.
A link checking site is one to which you submit the address of a web page; it will store this address in a database and will then periodically check that the document is still accessible. If it discovers that a document is no longer available then it will email the customer who asked for the site to keep an eye on the document.
This is the type of service that technical staff who look after a collection of web documents find valuable; such staff, often known as webmasters (a term applied to both male and female staff, although the equivalent female term webmistress is very occasionally used), need to know very quickly when this happens. For example, the page that is no longer accessible could be the home page for a company that sells some goods through the internet: having web documents unavailable means that it effectively shuts the front door of the store to customers. Because speed in this case is essential a number of link checking sites offer webmasters a notification service via a customer's portable phone or pager.