The "secret" of Google's early success in producing superior search results was due to a system of rating pages by the pages that linked to them, which they called PageRank.
While the mathematical formulas tend to be complex, the basic concept of PageRank (trademarked by Google) is fairly easy to understand. Each page on the web gets PageRank (PR) from pages that link to it; simultaneously, each page on the web gives PR to other pages that it links to. PageRank ranges from 0 to 10, with 10 being awarded to massively linked pages while 0 might be awarded to pages with no external linkage.
The PageRank approach put Google light-years ahead of their competition who was primarily focused on the content of pages and websites. A specialist is search engine optimization could no longer "crack" the algorithm to create pages that would instantly rank well for any keyword or search phrase. In addition to PR, Google also used the anchor text of inbound links to determine what the page was about.
Of course, SEOs reacted to the PageRank initiative. They launched link development campaigns to build links for sites they were promoting. In some cases, they used crosslinking of controlled sites or link farms to rapidly create links. To counter this, Google has adjusted its use of PR and its overall algorithm, as well as taking steps to detect artificial PageRank manipulation.
Regardless of what happens in the arms race between search engines and optimizers, links and PageRank seem likely to play a continued role.
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