How do search engines work?

… it’s very complicated.

As Google compiles its index, it calculates a number it calls PageRank for each page it finds. This was the key invention of Google’s founders, Mr. Page and Sergey Brin. PageRank tallies how many times other sites link to a given page. Sites that are more popular, especially with sites that have high PageRanks themselves, are considered likely to be of higher quality.

[The interviewee] has developed a far more elaborate system for ranking pages, which involves more than 200 types of information, or what Google calls “signals.”

Google Keeps Tweaking Its Search Engine By Saul Hansell
June 3, 2007

… and it’s usually kept secret.

Google and other search engines want to be better than their competition

  • The relevance of search results is a huge part of their product and how good their algorithm is becomes their competitive advantage 
  • Primary source of income is by selling ads alongside search results, the more relevant the search result, the more relevant the accompanying ads, the more likely they will be clicked on

Search engines want to reduce the effects of Search Engine Manipulation or “Black Hat” SEO

If you know how an algorithm works, you can figure out how to game the system.

What is SEO Manipulation –

Spamdexing – Wikipedia