The links on Web pages connect to other Web pages. Some of the pages could be on the same Web server while others can be anywhere else on the Web. This great strength of the Web is also a weakness, in that a company can never know every Internet site, intranet page, or bookmark list that links to its pages. And thus, it is impossible to update every page linking to its pages. A Web page dies every time that one or more files on a Web server have their names changed, their location in the subdirectory structure moved, or their host names modified.
Links also die when a server name changes.
Then again, there are plenty of pages, directories, and sites that have just been removed. End of story. An organization may cease to exist, stop paying its Web bills, or get cut off by its hosting company. Once again, all the links pointing to those pages then die. Links from the Net portals and search engines are another huge source of dead links.