How do search engines work?

Search engines work in three main stages. First, automated programs called crawlers or spiders, such as Googlebot, follow links from page to page and download content. Second, the pages are analysed and stored in an index; the Google index contains hundreds of billions of web pages and is well over 100 million gigabytes in size. Third, when you type a query, ranking algorithms sort matching pages using hundreds of signals, including relevance, page quality, freshness, location and how other sites link to them. Google founders Larry Page and Sergey Brin built their success on PageRank, a 1998 algorithm that treated links as votes.