How Does A Search Engine Work?

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You probably use search engines every day. From looking up words you don’t understand to searching for a purchase, search engines make finding that one piece of information on the Internet possible. They sort out all of the billions of pieces of data and find only the bits that are of interest of you. Search engines do all of this work in under a second. Have you ever stopped to consider how search engines work?

There are two different types of systems utilized by the various search engines to filter information. The first is a system under which humans actually review and index sites themselves. This method is obviously not very efficient and is not used by any of the major search engines. Those search engines like Yahoo, Bing and Google turn to the second method †which is automated. Typically referred to as crawler based, these systems use ‘spidered’ to ‘crawl’ new website and to follow links. These spiders are constantly searching the Internet and reporting to a control module. This module not only provides the spiders with instructions, ...
... it also collates the data.

Once a website has been ‘crawled’ it is indexed. During this process, a module records specific data about a webpage. Information such as keywords, URLS and other relevant information are combined with other sites to create a huge table that can be easily referenced during the search process. Because the search results are based on this index, it is critical that websites are indexed.

Finally, a search engine uses the information received from the above two steps to create a list of the most relevant websites. The information is based on a predetermined set of criteria. While we know some of the components of the formula used to rank sites, the actual formulas are highly guarded and secret. It is safe to say that the results from a particular search are based, at least in part, on the following:

1. Keywords
2. Site maps
3. Links
4. Content density

The search engine algorithm uses this information, found in the index table, to rank each site. This is the ‘rank order’ of your search results. It is important to note that most search engines include several paid advertisements with organic results. These ads are selected based on a bidding system.

Understanding how a search engine gets results is about a lot more than wondering why you get directed to particular sites. It is actually one of the best ways to understand website design and development. By understanding how search engines view websites and what they do with that information, you can begin to see how your website must be designed and built to attract the spiders. If your site is never indexed, it will never appear on a search engine results page.

Without search engines, the Internet would be an impossible to navigate quagmire of information. Search engines and their constantly crawling spiders allow us to find the information we need with a minimum of fuss.