PageRank (PR)

Google Search's patented system for ranking web pages is PageRank. PageRank is a unique algorithm developed at Stanford University (by Google co-founder Larry Page) and licensed to Google. PageRank is largely responsible for the success of Google. PageRank is more effective than many other search engine algorithms at identifying spam, keyword stuffing, and other types of black hat SEO techniques. PageRank is effective at weeding out valid and invalid search results. In short, you are more likely to find what you want using Google Search than other search engines, particularly in comparison to other search engines around in the year 2000. As a result of PageRank's success, more people use Google when searching for information on the world wide web than any other search engine.

When you enter a search term like "dry cleaning" in Google Search, there are thousands—often millions—of results. Some results are useless, irrelevant pages full of spam (web pages that have included that term just to get traffic, even though they aren't discussing dry cleaning or offering dry cleaning services). Other web pages are useful only to a small, select geographical location (such as a dry cleaner in Denver, Colorado). PageRank manages to weed through a lot of this, displaying first those results it deems most likely to be what you're looking for. In addition, PageRank has ways of detecting when a web page is spamming a search engine, thus sifting out the more obvious irrelevant websites from the top results.

PageRank works based on keywords, Inbound links, Outbound links, and other factors. PageRank assigns a "relevance" number between 1 and 10 to each webpage that contains that keyword. Web pages are ranked using a number of factors, including the number and quality of Inbound links (the assumption being that the more high-ranking websites that give links to web page A, the more likely web page A is to be relevant and contain useful information). The most relevant web pages are given scores close to 10, while the least relevant web pages have scores close to or at 0.

Prior to PageRank, most search engines had much more primitive (and easily manipulated) methods for determining the order they display search results on Search Engine Results Page (SERP). At the time PageRank was developed (late 1990's), nearly all search engines ranked web pages solely on the number of times a keyword was listed on a page. Naturally, this weakness was often exploited by less honorable webmasters, who included long lists of keywords (spamming the search engine) so that web pages could leap up on the Search Engine Results Page (SERP). The results generated by search engines had become very unreliable by the late 1990s. Google Search's PageRank outstripped the competition because it offered ease of use and (most importantly) more reliable search results to users on the world wide web.