How Do Search Engines Work?

How do search engines work? Let’s find out

Contents

Search engines work by crawling billions of pages with web crawlers. Also known as spiders or bots, crawlers navigate the web and follow links to find new pages. These pages are then added to an index that search engines pull their results from.
If you do SEO, understanding how search engines work is essential. After all, it is hard to optimize for something when you don’t know how it works.

That is what you will learn in this guide.

Search engine basics

Let’s start by looking at what search engines are, why they exist, and how they make money.

What are search engines?

Search engines are searchable databases of web content. They are made up of two main parts:

1. Search index: Think of it as a digital library of information about web pages.
2. Search algorithms: Think of them as the computer program(s) tasked with matching results from the search index.

What is the aim of search engines?

Every search engine aims to provide the best, most relevant results for its users. That is, in part, how they gain market share. 

How do search engines make money?

Search engines have two types of search results:

1. Organic results from the search index: You can’t pay to be here.
2. Paid results from advertisers: You can pay to be here.

Every time someone clicks a paid search result, the advertiser pays the search engine. This is known as pay-per-click (PPC) advertising, and it is why market share matters. More users mean more ad clicks and more revenue.  

How do search engines build their indexes?

Every search engine has its own process for building a search index. Below is a simplified version of the process Google uses.

Let’s go into the details.

URLs

It all starts with a list of known URLs. Google discovers these in many ways, but the three most common are:

1. Backlinks: Google has an index of hundreds of billions of web pages. If someone links to a new page from a known page, Google can find it from there.
2. Sitemaps: Sitemaps tell Google which pages and files on your site you consider important.
3. URL submissions: Google lets site owners request crawling of individual URLs in Google Search Console.

Crawling

Crawling, also called spidering, is where a computer bot visits and downloads known URLs. Google’s crawler is Googlebot. 

Processing and rendering

Processing is where Google works to understand and extract key information from crawled pages. To do this, it has to render the page, which means running the page’s code to understand how it looks to users. Nobody outside Google knows every detail of this process. But that doesn’t matter. All we really need to know is that it involves extracting links and storing content for indexing.

Indexing

Indexing is where processed information from crawled pages is added to the search index. The search index is what you search when you use a search engine. That is why being indexed in major search engines like Google and Bing is so important. Users can’t find you unless you are in the index. Did you know? According to research from January 2023, Google holds 91.43% of the search engine market. Because it is the search engine most people use, it can send you more traffic than the others.

How do search engines rank pages, and on what basis?

Discovering, crawling, and indexing content is only the first part of the puzzle. Search engines also need a way to rank matching results when a user runs a search. This is the job of search algorithms. 

What are search algorithms?

Search algorithms are formulas that match and rank relevant results from the index. Google uses many factors in its algorithms. 

Key Google ranking factors

Nobody knows every Google ranking factor, because Google has not disclosed them. But we do know some of the important ones. Let’s look at a few.

Backlinks

Backlinks are links from a page on one website to another. They are among Google’s strongest ranking factors. That is probably why a study covering more than a billion pages found a strong correlation between linking domains and organic traffic.

Still, it is not all about quantity. Quality matters too. Pages with a few high-quality backlinks often outperform pages with many low-quality ones.

Relevance

Relevance is how useful a given result is to the searcher. Google has many ways of determining this. At the most basic level, it looks for pages containing the same keywords as the search query. It also looks at engagement data to see whether others found the result helpful.

Freshness

Freshness is a query-dependent ranking factor. It is stronger for searches that call for fresh results. That is why, for example, you see recently published pages at the top for “Sakarya web design.”

Page speed

Page speed is a ranking factor on desktop and mobile. However, it is more of a negative ranking factor than a positive one. That is because it penalizes the slowest pages rather than rewarding lightning-fast ones.

Mobile-friendliness

Mobile-friendliness has been a ranking factor on mobile and desktop since Google’s move to mobile-first indexing in 2019. 

How do search engines personalize results?

Google tailors search results to each user. To do so, it uses information such as your location, language, and search history. Let’s take a closer look at these.

Location

Google uses your location to personalize results for searches with local intent. That is why all the results for “Web Design Agencies” come primarily from local agencies. Google knows you are unlikely to go to Japan for web design services.

Language

Google knows there is no point in showing Turkish results to Spanish users. That is why it ranks localized versions of content (where available) for users who speak different languages.

Search history

Google saves the things you do and the places you go in order to give you a more personalized search experience. You can opt out of this, but most people probably don’t.  

What have we learned about how search engines work?

• A search engine consists of two main parts: the index and the algorithms.
• To build its index, it crawls known pages and follows links to find new ones.
• The aim of search algorithms is to return the best, most relevant results.
• The quality of search results is important for building market share.
• Nobody knows all of Google’s ranking factors for organic results.
• Key ranking factors include backlinks, relevance, and freshness.
• Google personalizes its results based on your location, language, and search history.