I think Mr Venkiteswaran has already given the requisite details very nicely but I want to add some general things in this context. There are a large number of sites in internet which are providing information to the visitors or surfers and are earning some money through the advertisement display in their pages. It is obvious that more and more people come to that site, more the advertisement will be exposed to the customers and the visual marketing of the product or service will take place. A visitor will come back to site time and again if he finds good quality information there. That is the reason why the site editors or owners are concerned for the quality and content. In addition to the quality, volume is also a criterion because if some person does not find an information elsewhere but gets it here then that is a commendable thing and we all have to contribute here with that in our mind so that it becomes a niche site in educational matters.
Knowledge is power.