Web 2.0
 To allow users to continue to interact with the page, communications such as data requests going to the server are separated from data coming back to the page. Otherwise, the user would have to routinely wait for the data to come back before they can do anything else on that page, just as a user has to wait for a page to complete the reload. This also increases overall performance of the site, as the sending of requests can complete quicker independent of blocking and queueing required to send data back to the client. some web 2.0 sites : YouTube, last.fm, eBuddy, flickr, blogger, reddit, skype, gamesnips, littlewiki.
Some advantages of web 2.0 are that it cost less, it is more flexibal in the possibility of choosing technologies, it has easier and faster access to information when and where it is needed, the integration of a variety of technologies in the teaching-learning activites.
Some disadvantages are then an internet connection is required, it leads to a low quality of the actual content, it gives everyone the opportunity to complain, thus creating a community without rules and it has limited security. is associated with web applications that facilitate participatory information sharing on the world wide web. A Web 2.0 site allows users to interact and collaborate with each other in a social media dialogue as creators of user-generated content in a virtual community, in contrast to websites where users are limited to the passive viewing of content that was created for them. Web 2.0 websites allow users to do more than just retrieve information. By increasing what was already possible in "web 1.0", they provide the user with more user-interface, software and storage facilities, all through their browser. This has been called "Network as platform" computing. Users can provide the data that is on a Web 2.0 site and exercise some control over that data.