Flash is a set of technologies that enable programmers to create interactive Web pages. It's a technology that uses vector graphics. Vector graphics record image data as a collection of shapes and lines rather than individual pixels, which allows computers to load Flash images and animation faster than pixel-based graphics.
Flash files stream over the Internet, which means the end user accessing the file doesn't have to wait for the entire file to download to his or her computer before accessing parts of it. With Flash-based programs like YouTube's video player, this means you can start watching a film clip without having to download it first.
More than 98 percent of all computers connected to the Internet have a Flash player installed [source: Adobe]. That makes Flash an attractive approach for many programmers. They can create a Web OS knowing that the vast majority of computer users will be able to access it without having to download additional software.
The "asynchronous" aspect of AJAX means that AJAX applications transfer data between servers and browsers in small bits of information as needed. The alternative is to send an entire Web page to the browser every time something changes, which would significantly slow down the user's experience. With sufficient skill and knowledge, a programmer can create an AJAX application with the same functions as a desktop application.
Like Flash, most computers can run AJAX applications. That's because AJAX isn't a new programming language but rather a way to use established Web standards to create new applications. As long as an application programmer includes the right information in an application's code, it should run fine on any major Web browser. Some well known Web applications based on AJAX include Google Calendar and Gmail.
Why would anyone want to use a Web OS? Keep reading to find out.