Types of Search Engine:  

Some of the basic categories of Search engines are : 

a. Primary Search Engines: Such search engines use web crawlers or spiders to traverse the web and scan websites for key words, phrases, to generate database of web pages having some indexing or classification. Google and Alta Vista are examples of primary search engines. 

b. Web directory: Web directories organize information into categories and subcategories or directories. You can search a web directory for all those entries that contain a particular set of keywords. Directories differ from search engines in the way they organize information. Yahoo is an example of web directory. 

c. Meta search engines: Such search engines pass your queries to many search engines and web directories and present summarized results to the users. Some of the examples of meta search engines are - Dogpile, Infind, Metacrawler, Metafind and Metasearch.