With a decent understanding of how search engines work and how people use those search engines, you can now concentrate on some more detailed information about these engines. For example, you already know that all search engines aren’t created equal, but did you know that there are different types, or classifications, of search engines? Search engines can be broken down into three different types (in the broadest of terms): primary, secondary, and targeted.
Primary search engines
A primary search engine is the type you think of most often when search engines come to mind. Some index most or all sites on the Web. For example, Yahoo! Google, and MSN are primary (also called major) search engines. Primary search engines generate the majority of the traffic to your web site, and as such they will be the primary focus of your SEO efforts. Each primary search engine differs slightly from the others. For example, Lycos has been around much longer than Google, yet Google is the most popular search engine on the Web. Why is that? Most likely, it’s because people find that Google provides better search results.

The difference between those search results lies in the search algorithm used to create the search engine. Most primary search engines are also more than just search. Additional features such as e-mail, mapping, news, and different types of entertainment applications are also available from most of the primary search engine companies. These elements were added long after the search feature was established as a way to draw increasing numbers of users to the search engine. Although those features don’t change the way people search, they might affect which search engine people choose.

Google Overview
Each of the major search engines differs in some small way. Google is the king of search engines, in part because of the accuracy with which it can pull the results from a search query. Sure, Google offers all kinds of extras like e-mail, a personalized home page, and even productivity applications, but those value-added services are not what made Google popular.

What turned Google into a household word is the accuracy with which the search engine can return search results. This accuracy was developed when the Google designers combined keyword searches with link popularity. The combination of keywords and the popularity of links to those pages yields a higher accuracy rank than just keywords alone. Of course, it also helps that Google places paid advertisements in a separate part of the page, as obvious ads, and not as part of the actual search results. However, it’s important to understand that link popularity and keywords are just two of dozens of different criteria that search engines can use in ranking the relevancy of web pages.
Yahoo! Overview
Most people know that Yahoo! is a search engine, but it’s also a web directory, which basically means that it is a list of the different web pages available on the Internet, divided by category and subcategory. In fact, few people know that Yahoo! started as the favorites list of the two young men who founded it. Through the acquisition of companies like Inktomi, All the Web, AltaVista, and Overture, Yahoo! gradually gained market share as a search engine.
Yahoo!, which at one time used Google to search its directory of links, now ranks pages through a combination of the technologies that it acquired over time. However, Yahoo!’s link-ranking capability is not as accurate as Google’s. In addition, Yahoo! has a paid-inclusion program, which some users think tends to skew search results in favor of the highest payer.
MSN Overview
MSN’s search capabilities aren’t quite as mature as those of Yahoo! or Google. As a result, MSN has not yet developed the in-depth link analysis capabilities of these other primary search engines. Instead, MSN relies heavily on web site content for ranking purposes. However, this may benefit new web sites that are trying to get listed in search engines.
The link-ranking capabilities of Google and Yahoo! can preclude new web sites from being listed for a period of time after they have been created. This is because (especially where Google is concerned) the quality of the link may be considered during ranking. New links are often ignored until they have been in place for a while. Because MSN relies heavily on page content, a web site that is tagged properly and contains a good ratio of keywords will be more likely to be listed — and listed sooner — by the MSN search engine. Therefore, though it’s not the most popular of search engines, MSN is one of the primaries, and being listed there sooner rather than later will help increase your site traffic