Search Engine Algorithm

In order to succeed with search engine optimization (SEO), it's important to understand how search engines algorithms work. Many site owners jump feet first into SEO by building backlinks, posting content, and optimizing meta tags. While these are important steps to help your site get search engine visitors, understanding how Google, Bing, and the other major search engines interpret these actions can make your SEO efforts more effective.

Here is a brief guide to search engine algorithms: their past, present, and potential future.

In The Beginning...

Before search engines came along, people largely used web directories to find information on the web. When you wanted to learn a new cookie recipe, you would head over to a directory like DMOZ.org and sift through the results in the "baking" category:

DMOZ Listing

Because directory listings were hand-curated by humans with a set of rigid standards, the quality of the pages listed in most directories tended to be quite high.

However, as the web exploded, there were simply too many pages for directories to keep up with...

Enter the Search Engine

Old Yahoo Homepage

In the early days of search engines, sites like AltaVista.com and Yahoo! rose to prominence by becoming the first to allow users to search their index of web pages.

Unlike directories, which relied on humans to submit and review pages, search engines used "spiders" to automatically catalog (or "index") the web. And this index could be easily searched by entering certain "keywords". Based on what keywords you used, the search engines would bring up a set of relevant results. The search function and the automation behind the results allowed users to get a higher variety of results faster than they could from a human-curated directory.

Amazingly, the fundamentals of how search engines operate are more or less the same today: when you perform a search in Google you're not actually searching the live internet. You're searching Google's index of the web as it appeared the last time a spider visited the page.

However, early search engines were 100% reliant on a page's relevancy to sort and rank their results. Continuing our cookie recipe example from above, if you were to search an old search engine for "cookie recipes", your results would be sorted by how many times the words "cookie recipe" appeared on the page and how often the page had "cookie recipe" in their meta tags.

This made older search engines incredible easy to manipulate. Over time, the results were cluttered with keyword-stuffed pages that lacked the quality users wanted.

Google Changes the Game

Google Homepage Old School

In 1998, two Stanford computer science students -- Larry Page and Sergey Brin -- created a revolutionary search engine algorithm nicknamed "BackRub".

What made their search engine different was that -- in addition to the relevancy signals other search engines used -- Google also factored in a quality signal.

That quality signal was known as PageRank (named after Larry Page). PageRank measures how many hyperlinks are pointing to a page and the authority of each of the links pointing to that page. For the first time users saw the best results for a given search, not only the most relevant.

However, as people became wise to the PageRank algorithm, people worked hard to game the Google algorithm by setting up "link farms": websites that exist solely to link to other websites. In response to the widespread use of link farms, Google figured out ways to identify link farms and devalue links coming from them: a cat and mouse game that continues to this day.

Today, Google makes over 500 changes to its algorithm every year.

Present and Future

Today, search engines are leagues more sophisticated than they were in the early days. Google now uses over 200 ranking signals to sort through its results, which includes how often a page is shared on social media sites like Facebook and whether or not people bookmark a page in the Google Chrome web browser.

What does the future hold for search engine algorithms?

Google and Bing are moving heavily towards personalized search results. Instead of having the same 10 results shown to every user, results will be tweaked based on your browsing history, people you follow on social media sites and maybe even your shopping habits!

Authorship is a hot topic in SEO at the moment. In the future, search engines may pay less and less attention to a page's authority and put more emphasis on who wrote the content on that page.

Helpful Resources

If you'd like to learn more about how search engine algorithms work, here are a few helpful resources:

The Anatomy of a Search Engine:
The original overview of the first Google algorithm. Surprisingly readable.

How Search Works:
Google's incredible visual guide to how their search engines work.

An Overview of Google's 200 Ranking Factors:
An unofficial list of the 200 factors Google uses to rank pages in their index.

Google Algorithm Change History:
SEOMoz keeps track of all, or at least, most of Google's algorithm update here.

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