| is an ad serving program run by Google. Website | | | | How AdSense works: |
| owners can enroll in this program to enable text, | | | | Each time a visitor visits a page with an AdSense |
| image and, more recently, video advertisements | | | | tag, a piece of JavaScript writes an iframe tag, |
| on their sites. These ads are administered by | | | | whose src attribute includes the URL of the page. |
| Google and generate revenue on either a per-click | | | | Google's servers use a cache of the page for the |
| or per-thousand-impressions basis. Google is also | | | | URL or the keywords in the URL itself to |
| currently beta-testing a cost-per-action based | | | | determine a set of high-value keywords. (Some |
| service. | | | | of the details are described in the AdSense |
| Google utilizes its search technology to serve ads | | | | patent.) If keywords have been cached already, |
| based on website content, the user's geographical | | | | ads are served for those keywords based on the |
| location, and other factors. Those wanting to | | | | AdWords bidding system. |
| advertise with Google's targeted ad system may | | | | The storage requirements of an AdSense system |
| sign up through AdWords. AdSense has become a | | | | are stunningly modest. If each URL has just 8 |
| popular method of placing advertising on a | | | | "high-value" keywords, each represented by a |
| website because the ads are less intrusive than | | | | single 32-bit number, then the keywords for each |
| most banners, and the content of the ads is | | | | URL could be represented with just 32 bytes. The |
| often relevant to the website. | | | | high value keywords of 4 billion URLs could be |
| It currently uses JavaScript code to incorporate | | | | stored in 128GB, which would cost only $100 |
| the advertisements into a participating site. If it is | | | | (circa 2006). 400 billion URLs or 100 drives (for a |
| included on a site which has not yet been crawled | | | | redundancy of 100) would require only $10,000 in |
| by the Mediabot, it will temporarily display | | | | storage costs. |
| advertisements for charitable causes known as | | | | AdSense serves a very large number of pages |
| public service announcements (PSAs). (Note that | | | | each day. If each day around 1B people saw 10 |
| the Mediabot is a separate crawler from the | | | | AdSense impressions (or 100M people saw 100 |
| Googlebot that maintains Google's search index.) | | | | AdSense impressions), then AdSense would serve |
| Many sites use AdSense to monetize their | | | | around 10B requests/day, or 115,741 requests |
| content and some webmasters work hard to | | | | sec. If one machine can serve 20 reqs/second |
| maximize their own AdSense income. They do | | | | (seek times to read a random 4096-byte location |
| this in three ways: | | | | on a drive allow for bursts of well over 100 reqs |
| 1. They use a wide range of traffic generating | | | | second), then Google would require 5,787 servers |
| techniques including but not limited to online | | | | to serve these 10B reqs/day. If each of these |
| advertising. | | | | servers were hosted at a cost of $100/month, |
| 2. They build valuable content on their sites; | | | | then it would cost $579K/month to run the |
| content which attracts AdSense ads and which | | | | adservers needed. |
| pay out the most when they get clicked. | | | | Suppose these 10B impressions/day generated |
| 3. They use copy on their websites that | | | | clicks at a clickthrough rate of .3% and an |
| encourage clicks on ads. Note that Google | | | | average CPC of $.10. Then each day Google |
| prohibits people from using phrases like "Click on | | | | would receive 30M clicks/day (347 clicks/sec), |
| my AdSense ads" to increase click rates. Phrases | | | | generating $3M/day ($34.77/sec), or 900M clicks |
| accepted are "Sponsored Links" and | | | | month, generating $90M/month. |
| "Advertisements". | | | | Abuse: |
| The source of all AdSense income is the | | | | Some webmasters create sites tailored to lure |
| AdWords program which in turn has a complex | | | | searchers from Google and other engines onto |
| pricing model based on a Vickrey second price | | | | their AdSense to make money from clicks. These |
| auction, in that it commands an advertiser to | | | | "zombie" sites often contain nothing but a large |
| submit a sealed bid (not observable by | | | | amount of interconnected, automated content |
| competitors). Additionally, for any given click | | | | (e.g. a directory with content from the Open |
| received, advertisers only pay one bid increment | | | | Directory Project). Possibly the most popular form |
| above the second-highest bid. | | | | of such "AdSense farms" are splogs ("spam |
| AdSense for feeds: | | | | blogs"), which are centered around known |
| In May 2005, Google unveiled AdSense for feeds, | | | | high-paying keywords. Also many sites use free |
| a version of AdSense that runs on RSS and | | | | content from other web sites, such as Wikipedia, |
| Atom feeds that have more than 100 active | | | | to attract visitors. These and related approaches |
| subscribers. According to the Blog, "advertisers | | | | are considered to be search engine spam and can |
| have their ads placed in the most appropriate | | | | be reported to Google. |
| feed articles; publishers are paid for their original | | | | Criticism: |
| content; readers see relevant advertising and | | | | Due to concerns about click fraud, Google |
| in the long run, more quality feeds to choose | | | | AdSense has been criticized by some SEO firms |
| from". | | | | as a large source of what Google calls "invalid |
| AdSense for feeds works by inserting images into | | | | clicks". In response, Google says that it "removes |
| a feed. When the image is displayed by the | | | | publishers from their partner network on a daily |
| reader/browser, Google writes the ad content | | | | basis". Some disabled publishers have complained |
| into the image that it returns. The ad content is | | | | that the process is not transparent or |
| chosen based on the content of the feed | | | | accountable. |
| surrounding the image. When the user clicks the | | | | To help prevent click fraud, publishers can choose |
| image, he or she is redirected to the advertiser's | | | | from a number of click tracking programs. These |
| site in the same way as regular AdSense ads. | | | | programs will display detailed information about |
| AdSense for search: | | | | the visitors who click on the AdSense pages. |
| A companion to the regular AdSense program, | | | | Publishers can use that data to determine if |
| AdSense for search lets website owners place | | | | they've been a victim of click fraud or not. There |
| Google search boxes on their pages. When a user | | | | seems to be many such commercial scripts |
| searches the web or the site with the search | | | | available. An open-source alternative is AdLogger. |
| box, Google shares any ad revenue it makes | | | | Google has also come under fire for not doing |
| from those searches with the site owner. | | | | enough to combat the misuse of trademarks. |
| However, only if the ads on the page are clicked, | | | | Since 2004, Google had stopped prohibiting |
| the publisher is paid. Adsense does not pay | | | | advertisers from bidding on any keyword, including |
| publishers for mere searches. | | | | trademarked terms. |