the WEB-7
Caches: on strategic positions in the network, specialized servers analyzes the http traffic and keep a copy of the often requested documents. When asked again for a cached document, they give directly the copy to lower the network load.
Indexers: Some specialized applications, the robots, explore the web, following every URL and keeps an index of the words in a database. The content of these indexes can be queried on a web server. A well known example is www.google.com