How do search engines work?

Everyone knows what a search engine does, but far fewer people actually know how they work. Most people are content with entering in a search term, clicking the search button, and then receiving a list of webpages that are relevant to their search. What goes on in the black box is of little concern to them. But what happens when a search is conducted is that a series of complex mathematical algorithms take place in milliseconds to populate all the content that the search engine deems relevant to a search term.

Now, I’m not going to go into detail about the algorithms used by Google or Bing, but I will provide the high-level basics of how search engines work. Having a basic understanding of how search engines work can provide you with valuable information to improve your SEO techniques. There are three major components that search engines use to operate and provide accurate search results that are ranked in order of relevance and importance.

1. Crawling

Search engines use robots called “spiders” or “crawlers” that crawl around the web and look for content. Spiders are bits of computer code that find information on a web page, read it, and then follow links from your web page to other pages.

Search engines will periodically re-crawl webpages to look for changes to the original page. This means that you can modify your content and the search engine spiders will re-evaluate your web pages.

If a spider cannot see your content, or doesn’t understand what it is about, then it cannot index the web page and therefore it will not rank the page. Clean, fast-loading code matters and spiders can determine if a website is well made with clean website architecture.

2. Indexing

When the spider reads content it indexes the information it collects in a giant hard drives. They decipher the code from the web pages and store selected pieces that can be recalled later when needed for a search query. Search engines have massive datacenters all over the world so that billions of pages can be accessed in fractions of a second.

3. Ranking

Search engines crawl and index billions of web pages so that they can populate search results pages in the blink of an eye. But how search engines rank the results is where the true magic takes place. Google, Bing, Yahoo, and other search engines all function to provide users with results that are both relevant and authoritative, or more simply, they seek to provide the best results.

When a user enters a search term, search engines will scour the billions of web pages that have been indexed and return only results that are relevant to the search query. They take only the relevant web pages and then rank these pages in order of perceived usefulness using their complex mathematical algorithms.

Search engines use hundreds of factors to determine the relevance of web pages to given searched words or phrases. In the earlier days of the Internet, search engines would only take in a few factors and concentrated on providing pages with the right words. Nowadays, search engines are continually updating their methodologies to finer tune their search results.

When determining a web page’s authority, major search engines typically use the popularity of the page. The assumption being that the popularity of a web page corresponds with the value of the information that it provides. As with a web page’s relevance, there are many factors that search engines use to determine the popularity of a page. They range from factors regarding the websites that link to the web page, to social media metrics such as how often the page has been shared on Twitter, Facebook, etc.

Each year for the past 6 years, SEOmoz, which is a leading authority in the SEO community, conducts analysis to provide information on the Search Engine Ranking Factors. The chart below provides information on the major factors that search engines use to determine how they rank web pages.

Ranking Algorithm

Ranking Algorithm

Catering to these factors is therefore the essence of search engine optimization or SEO. As the search engines continue to update their algorithms and improve their ranking methodology, individuals responsible for updating their company’s website need to make sure that they are addressing these factors in order for their web pages to rank well. This is why SEO is the most critical aspect of internet marketing because if a website is not optimizing its’ web pages to address the factors that the search engines are using to rank them, then they will not get found online.

Search engines work by crawling the Internet, indexing the content that they find from web pages and then providing relevant results that are ranked in order of importance. And having an understanding of this process goes a long way in implementing strategies to rank web pages higher on search engine result pages.


  1. I’m not certain where you’re getting your info, but great topic.
    I must spend some time learning much more or understanding more.
    Thanks for fantastic information I used to be
    searching for this info for my mission.

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