Just how big is the Web, anyway? And how much of it do the search engines crawl?
It's been ages since I've seen anyone try to estimate the size of the Web. Now, a new paper puts it at 11.5 billion pages or more for January 2005.
The paper, from Antonio Gulli of Università di Pisa (who is also director of advanced products for Ask Jeeves) and Alessio Signorinialso of the University of Iowa, estimates what percentage of the Web is covered by each search engine:
|Search Engine||Self-Reported Size (Billions)||EstimatedSize (Billions)||Coverage of Indexed Web (%)||Coverage of Total Web (%)|
|Note: "Indexed Web" refers to the part of the Web considered to have been indexed by search engines.|
The first thing you wonder is whether any of the search engines are lying about their size. Google claims to have the biggest search index, 8.1 billion pages. The estimate shows Google's claim is pretty much on target. The same holds true for MSN and Ask Jeeves.
Yahoo doesn't provide an estimate of its index. The figure in the table dates back to 2004, when it said it was comparable to Google. The paper's estimate is useful, because we finally have an updated sense of where Yahoo might be.
There are a ton of caveats. Estimates are for the "visible" Web, URLs search engines can easily reach. The "invisible," or "deep," Web refers to content locked behind databases or other systems that search engines haven't extracted. I've seen estimates in the past that the deep Web might be 500 billion pages.
Though the study does some URL normalization, it still seems mirror or duplicate pages may have been counted. So though there may be a certain number of pages, the number of unique pages may be lower.
Finally, size shouldn't be a surrogate for relevancy. Having a ton of pages doesn't mean anything if you can't return the best pages in the top results. It's helpful to know a search engine has good Web coverage, but it's only one of many factors to consider.
It's still great to have some updated estimates of the Web's size, as well as search coverage. For background on size issues, see some historic articles on Search Engine Watch Search Engine Sizes page. I'm planning to update figures there, but the reference material is all still valid.
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