AdSense is an ad serving program run by Google. Website owners
can enroll in this program to enable text, image and, more
recently, video advertisements on their sites. These ads are
administered by Google and generate revenue on either a
per-click or per-thousand-impressions basis. Google is also
currently beta-testing a cost-per-action based service.

Google utilizes its search technology to serve ads based on
website content, the user's geographical location, and other
factors. Those wanting to advertise with Google's targeted ad
system may sign up through AdWords. AdSense has become a popular
method of placing advertising on a website because the ads are
less intrusive than most banners, and the content of the ads is
often relevant to the website.

It currently uses JavaScript code to incorporate the
advertisements into a participating site. If it is included on a
site which has not yet been crawled by the Mediabot, it will
temporarily display advertisements for charitable causes known
as public service announcements (PSAs). (Note that the Mediabot
is a separate crawler from the Googlebot that maintains Google's
search index.)

Many sites use AdSense to monetize their content and some
webmasters work hard to maximize their own AdSense income. They
do this in three ways:

1. They use a wide range of traffic generating techniques
including but not limited to online advertising.

2. They build valuable content on their sites; content which
attracts AdSense ads and which pay out the most when they get
clicked.

3. They use copy on their websites that encourage clicks on ads.
Note that Google prohibits people from using phrases like "Click
on my AdSense ads" to increase click rates. Phrases accepted are
"Sponsored Links" and "Advertisements".

The source of all AdSense income is the AdWords program which in
turn has a complex pricing model based on a Vickrey second price
auction, in that it commands an advertiser to submit a sealed
bid (not observable by competitors). Additionally, for any given
click received, advertisers only pay one bid increment above the
second-highest bid.

AdSense for feeds: In May 2005, Google unveiled AdSense for
feeds, a version of AdSense that runs on RSS and Atom feeds that
have more than 100 active subscribers. According to the Blog,
"advertisers have their ads placed in the most appropriate feed
articles; publishers are paid for their original content;
readers see relevant advertising -- and in the long run, more
quality feeds to choose from".

AdSense for feeds works by inserting images into a feed. When
the image is displayed by the reader/browser, Google writes the
ad content into the image that it returns. The ad content is
chosen based on the content of the feed surrounding the image.
When the user clicks the image, he or she is redirected to the
advertiser's site in the same way as regular AdSense ads.

AdSense for search: A companion to the regular AdSense program,
AdSense for search lets website owners place Google search boxes
on their pages. When a user searches the web or the site with
the search box, Google shares any ad revenue it makes from those
searches with the site owner. However, only if the ads on the
page are clicked, the publisher is paid. Adsense does not pay
publishers for mere searches.

How AdSense works: Each time a visitor visits a page with an
AdSense tag, a piece of JavaScript writes an iframe tag, whose
src attribute includes the URL of the page. Google's servers use
a cache of the page for the URL or the keywords in the URL
itself to determine a set of high-value keywords. (Some of the
details are described in the AdSense patent.) If keywords have
been cached already, ads are served for those keywords based on
the AdWords bidding system.

The storage requirements of an AdSense system are stunningly
modest. If each URL has just 8 "high-value" keywords, each
represented by a single 32-bit number, then the keywords for
each URL could be represented with just 32 bytes. The high value
keywords of 4 billion URLs could be stored in 128GB, which would
cost only $100 (circa 2006). 400 billion URLs or 100 drives (for
a redundancy of 100) would require only $10,000 in storage costs.

AdSense serves a very large number of pages each day. If each
day around 1B people saw 10 AdSense impressions (or 100M people
saw 100 AdSense impressions), then AdSense would serve around
10B requests/day, or 115,741 requests/sec. If one machine can
serve 20 reqs/second (seek times to read a random 4096-byte
location on a drive allow for bursts of well over 100
reqs/second), then Google would require 5,787 servers to serve
these 10B reqs/day. If each of these servers were hosted at a
cost of $100/month, then it would cost $579K/month to run the
adservers needed.

Suppose these 10B impressions/day generated clicks at a
clickthrough rate of .3% and an average CPC of $.10. Then each
day Google would receive 30M clicks/day (347 clicks/sec),
generating $3M/day ($34.77/sec), or 900M clicks/month,
generating $90M/month.

Abuse: Some webmasters create sites tailored to lure searchers
from Google and other engines onto their AdSense to make money
from clicks. These "zombie" sites often contain nothing but a
large amount of interconnected, automated content (e.g. a
directory with content from the Open Directory Project).
Possibly the most popular form of such "AdSense farms" are
splogs ("spam blogs"), which are centered around known
high-paying keywords. Also many sites use free content from
other web sites, such as Wikipedia, to attract visitors. These
and related approaches are considered to be search engine spam
and can be reported to Google.

Criticism: Due to concerns about click fraud, Google AdSense
has been criticized by some SEO firms as a large source of what
Google calls "invalid clicks". In response, Google says that it
"removes publishers from their partner network on a daily
basis". Some disabled publishers have complained that the
process is not transparent or accountable.

To help prevent click fraud, publishers can choose from a number
of click tracking programs. These programs will display detailed
information about the visitors who click on the AdSense pages.
Publishers can use that data to determine if they've been a
victim of click fraud or not. There seems to be many such
commercial scripts available. An open-source alternative is
AdLogger.

Google has also come under fire for not doing enough to combat
the misuse of trademarks. Since 2004, Google had stopped
prohibiting advertisers from bidding on any keyword, including
trademarked terms.

Ankit Talwar - Web Designer

About the author:
Ankit Talwar is the owner of www.Dead-Yahoo.com. He is a Web
Designer.