How Google Works

Here, then, is a guide to what happens during a typical Google search—now, of course, with automatic spell-check.

1. Query Box
It all starts with somebody typing in a request for information about the safest dog food, what time the D.M.V. closes, or what the prime rate is in China.

2. Domain-Name Servers
“Hello, this is your operator . . . ”
The software for Google’s domain-name servers runs on computers in leased or company-owned data centers all over the world, including one in the old Port Authority headquarters in Manhattan. Their sole purpose is to shepherd searches into one of Google’s clusters as efficiently as possible, taking into account which clusters are nearest to the searcher and which are least busy at that instant.

3. The Cluster
The request ­continues into one of at least 200 clusters, which sit in Google-owned data centers worldwide.

4. Google Web Server
This program splits a query among hundreds or thousands of machines so that they can all work on it at the same time. It’s the difference between doing your grocery shopping all by yourself and having 100 people simultaneously find one item and toss it into your cart.

5. Index Server
Everything Google knows is stored in a massive database. But rather than waiting for one computer to sift through those gigabytes of data, Google has hundreds of computers scan its “card catalog” at the same time to find every relevant entry. Popular searches are cached—held in memory—for a few hours rather than run all over again. That means you, Britney.

6. Document Server
After the index server compiles its results, the document server pulls all the relevant documents—the links and snippets of text from its massive database. How does Google search the Web so quickly? It doesn’t. It keeps three copies of all the information from the internet that it has indexed in its own document servers, and all those data have already been prepped and sorte