These are financially supported by advertising banners and licensing of their software. The advantage to these tools is that they are free and easy to access. The disadvantage is that these tools are very unsophisticated and don't yet take advantage of the more powerful search methods. Search tools can be loosely divided into several categories. Subject directories, search engines, specialty search engines and metasearch engines.
Subject directories are search tools that are organized by category.
Their system is similar to a filing cabinet containing folders with files in them. Subject directories are indexed and categorized by humans, not machines or software. Because of this their size tends to be smaller and they are not as up to date as some of the more powerful search engines. Users usually travel down a series of menus to search these sites, although keyword search is also available. They are not good for obscure topic searches.