Metasearch Engines Metasearch engines search more than one search engine at a time. They are good for finding the best resources on a common topic. They return to top hits from each search engine, but not the entire response from each search engine. Some have settings for numbers of hits returned and some filter out duplicates from the different search engines. Subject Directories Subject directories list selected Internet files categorized by broad or detailed subjects.
Many directories are on specific topics and many are very broad.
The most common example is Yahoo, however, there are many more directories, many compiled and evaluated by universities and aimed at researchers. The chart lists number of categories and whether the directories are searchable. Specialized database searches There are many specialized databases on the Internet. They cover topics from medicine, science to literature. Search engines that search narrow subjects are specialized directories.