AltaVista offers a family of search engines for different purposes and needs. Search, Advanced Search, and Raging Search all use the same database of Web sites, but they may display sites in different order or limit the search in special ways. Advanced Search displays the results in a random order unless you enter a term in the Sort box. The ranking algorithms used by Search and Raging Search are different. Search engines offered by other companies and organizations send out their own robots, build their own databases using their own inclusion criteria, and apply their own ranking algorithms.
Databases differ in size, coverage of the Web, and frequency of updates.
Engines differ also in their ability to apply filtering or screening commands, such as AltaVista's searches on Web page elements like titles, urls, links, text, and more. AltaVista prides itself on its rigor in excluding spam from your results. Given the size of the Web and all of these proprietary variables, you should expect differences in the results. Professional searchers often use several different search engines for their clients. For many other people, it makes sense to learn to use one search engine thoroughly and stick with it.