Each of these search tools actually searches its own database of Web pages. Choosing the right tools depends on what type of information you hope to find.
Directories contain sites that are submitted, reviewed and compiled by people.
They are assigned to an appropriate category or categories. While the database is smaller than one created by a search engine, they often provide better results because of the human role. As the name suggests, subject directories are lists that are categorized by topics and may be searchable by keyword. A software program called a spider or crawler automatically collects information from Web servers, indexes it, and creates a keyword-searchable database of Web pages. Because each search engine uses its own search method and because no search tool indexes the entire contents of the Internet, it is often helpful to use more than one tool to find information.