They are in competition with each other, so each one develops and uses different technologies to search through the roughly 800 million Web pages that exist on the internet. That is why a page is can have high ranking in one search engine and not even appear in another. The most complete search engine, NorthernLights, indexes only about one-sixth of what's out there. The trend is toward popular pages becoming more so, while new pages have an increasingly more difficult time being recognized.
Links boost the placement of the ranking.
InfoSeek has a more complex link popularity system that places emphasis on linking site status and relevancy. The use of meta tag keywords is favored by Altavista, Hotbot, Infoseek, Lycos and Web crawler. However AltaVista, Excite, Lycos, Netfind, NorthernLights and Web Crawler have low regard for meta tags descriptions or text in meta tags that exist alone without consistency. Hence, keywords have to be spread over the Web page, particularly near the end. So a front page with only images may look better but may suffer a lower ranking on some search engine results.