Computer-centric problems are the domain of high performance computing. The secret to these probems is "teraflops": as many as possible. Computer-centric applications can benefit from the Grid because it combines large computational resources allowing scientists to tackle problems that cannot be solved on a single system, or to solve problems much more quickly.

Data-centric problems are also called data-intensive problems and are the primary driving force behind the Grid. Huge amounts of scientific data are being created and the Grid will be used to collect, store and analyze this data in geographically distributed libraries and databases. Examples of data-centric problems include:

• Searching the terabytes of data generated every day by future high-energy physics experiments. The Grid will give thousands of physicists from hundreds of research institutes access to this data and power to analyze it.
• Studying the terabytes of astronomical photographic data collected by sky surveys and available in numerous network-accessible databases.
• Forecasting future climate using modern meteorological forecasting systems that move, process and assimilate gigabytes of data including remote satellite observations.

Community-centric problems are also referred to as collaborative applications and are concerned primarily with bringing people together to collaborate. They often comprise a "virtual shared space" where community members can share computational resources using the Grid. Community-centric problems range from interactive video conferencing to distributed musical concerts, to supporting collaborations of researchers trying to perform complex simulations using detectors from all over the world.

Real-time requirements

Real-time user interaction can enhance these applications and is a challenging aspect of Grid development. Here are some examples:

• The BoilerMaker system developed at Argonne National Laboratory allows multiple users to collaborate on the design of emission control systems in industrial incinerators. The different users can interact with each other and with a simulation of the incinerator. The simulation can be updated more quickly using Grid technology.
• The NICE system developed at the University of Illinois in Chicago allows children to participate in the creation and maintenance of realistic virtual worlds, for entertainment and education. Again, by distributing these virtual world simulations on a Grid, more users can benefit from the system.