豆知识 2010-05-16&05-22 Google三大核心业务之一：搜

 Hi. My name is Matt Cutts. I’m an engineer in the quality group of Google, and I’d like to talk today about what happens when you do a web search. 

 
 
The first thing to understand is that when you do a Google search, you aren’t actually searching the web, you’re searching Google’s index of the web, or at least as much of it as we can find. We do this with software programs called spiders. Spiders start by fetching a few webpages, then they follow the links on those pages and fetch the pages they point to and follow all the links on those pages and fetch the pages they link to and so on until we index a pretty big chunk 1 of the web. Many billions of pages stored across thousands of machines. 
 
 
Now, suppose I want to know how fast a cheetah 2 can run. I type in my search, say "cheetah running speed" and hit return. Our software searches our index to find every page that includes those search terms. In this case, there are hundreds of thousands of possible results. How does Google decide which few documents I really want? By asking questions, more than two hundred of them, like: How many times does this page contain your keywords? Do the words appear in the title, in the URL, directly adjacent? Does the page include synonyms 3 for those words? Is this page from a quality website or is a low quality, even spamming? What is this page’s page rank? That’s a formula invented by our founders 4 Larry Page and Sergey Brin that rates a webpage’s importance by looking at how many outside links point to it, and how important those links are. Finally we combine all those factors together to produce each page’s overall score, and send you back your search results about half a second after you submit your search. At Google, we take our commitment to delivering useful and impartial 5 search results very seriously. We don’t ever accept payment to add a site to our index, update more of them, or improve its ranking. 
 
 
Let’s take a look at my search results.
 
 
Each entry includes a title, a URL and a snippet of the text to help me decide whether this page is what I’m looking for. I also see links to similar pages, Google’s most recent stored version of that page, and related searches that I might want to try next. And sometimes along the right and at the top, I’ll see ads. We take our advertising 6 business very seriously as well. 
 
 
Both our commitment to deliver the best possible audience for advertisers, and to strive to only show ads that you really want to see. We’re very careful to distinguish your ads from regular search results. And we won't show you any ads at all if we can’t find any that we think will help you find information you're looking for, which in this case, the cheetah's top running speed is more than sixty miles an hour. 
 
 
Thanks for watching. I hope this made Google a little bit more understandable.