How Search Works

http://www.google.com/howgoogleworks | The life span of a Google query is less then 1/2 second, and involves quite a few steps before you see the most relevant results. Here's how it all works.

[typewriter keys clack]

[Matt Cutts]
Hi, my name is Matt Cutts.

I'm an engineer in the quality
group at 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 web pages
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've indexed a pretty big chunk
of the web,

many billions of pages stored
across thousands of machines.

Now, suppose I want to know
how fast a cheetah 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 200 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
for those words?

Is this page from a quality website
or is it low quality, even spamming?

What is this page's PageRank?

That's a formula invented by our founders,
Larry Page and Sergey Brin,

that rates a web page'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 search results
very seriously.

We don't ever accept payment
to add a site to our index,

update it more often,
or improve its ranking.

Let's take a look at my search results.

Each entry includes a title,
a URL, and a snippet of 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 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 the information

you're looking for
which, in this case,

the cheetah's top running speed,
is more than 60 miles an hour.

Thanks for watching,

I hope this made Google
a little bit more understandable.