Search engines have two major functions – crawling & building an index, and providing answers by calculating relevancy & serving results.
Through links, search engines’ automated robots, called “crawlers,” or “spiders” can reach the many billions of interconnected documents.
Once the engines find these pages, they next decipher the code from them and store selected pieces in massive hard drives, to be recalled later when needed for a search query. To accomplish the monumental task of holding billions of pages that can be accessed in a fraction of a second, the search engines have constructed data centers all over the world.
These monstrous storage facilities hold thousands of machines processing large quantities of information. After all, when a person performs a search at any of the major engines, they demand results instantaneously – even a 1 or 2 second delay can cause dissatisfaction, so the engines work hard to provide answers as fast as possible.
Search engines are answer machines. When a person looks for something online, it requires the search engines to scour their corpus of billions of documents and do two things – first, return only those results that are relevant or useful to the searcher’s query, and second, rank those results in order of perceived usefulness. It is both “relevance” and “importance” that the process of SEO is meant to influence. To a search engine, relevance means more than simply finding a page with the right words. In the early days of the web, search engines didn’t go much further than this simplistic step, and their results suffered as a consequence. Thus, through evolution, smart engineers at the engines devised better ways to find valuable results that searchers would appreciate and enjoy.