What is PageRank?
PageRank is an algorithm used by Google to rank web pages in their search engine results. It was invented by Larry Page and Sergey Brin, the founders of Google, at Stanford University in the 1990s.
The key idea behind PageRank is that a page is important or high-quality if it receives many inbound links from other high-quality pages.
This models the behavior of web users quite well - we tend to find good pages by following links from other good pages.
More technically, PageRank is a way of measuring the importance of website pages based on the link structure of the web.
Every web page is given an initial PageRank score. Then the PageRank of each page is recalculated based on the PageRank values of the pages linking to it.
Pages with more inbound links from other important pages receive a higher PageRank score.
PageRank is just one of many factors used by Google's ranking algorithms, but it was revolutionary in helping rank pages by quality rather than just keyword matching. PageRank was a major factor in Google's early success.
Imagine a tiny internet of just 4 web pages:
Page A links to pages B, C, and D.
Page B links to C.
Page C links to A.
Page D has no outbound links.
Initially, each page is given a PageRank of 1.
After the PageRank calculations, the new PageRank scores may look something like:
Page A: 3.6
Page B: 1.2
Page C: 2.4
Page D: 0.8
Page A has a high PageRank because it is linked to by an important page itself (C). Page D has a relatively low score since no pages link to it.
This is an extremely simplified example, but it illustrates how PageRank flows through the link structure, allowing important pages to be identified and ranked highly in search results.
Of course, the real web has billions of pages and Google's actual ranking system is much more complex, using machine learning and many other factors beyond just links. But PageRank helped revolutionize web ranking in the early days of search engines.