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High performance clusters and grids
On operating system level, two cluster architectures exist: High performance clusters and High availability clusters.
Clusters
High performance clusters are meant to create large computing power by combining many computer systems. Usually a large amount of cheap off-the-shelf PC's are used, connected by a high-speed network (gigabit Ethernet of Infiniband). This creates one large supercomputer.
These clusters are used for calculation-intensive systems, like weather prognosis, geological, nuclear of pharmaceutical investigations. The challenge is to have all systems doing useful calculations most of the time, without wasting resources and time communicating to other systems in the cluster.
0n www.top500.org a list of the world's 500 most powerful computers is published. Most of these systems really are clusters, based on a large amount of smaller systems. Many of these systems run Linux. A well-known high-performance open source project for Linux is Beowulf.
Grids
A Grid is a high-performance cluster that consists of systems that are geographically diverse. The limited bandwidth is the bottleneck when architecting grid systems. Therefore, grids can only be used for specific tasks.
The best known (and relatively old) example of a grid is the SETI@HOME project, where a large amount of PC's of Internet users are searching for extraterrestrial life. These type of grids use the unused computer time of PC's (for instance when the computer is showing it's screensaver). Tasks to be done can be distributed through the Internet and can be calculated on the idle PC's. When a piece of calculation is finished, the result will be sent back via the Internet and a new task can be retrieved.
Applications
A more serious example of a grid is a project that is searching for a cure for cancer or the analyses of the human DNA.
Broker firms exist for commercial exploitation of grids. People can get paid for contributing computer time, and companies can pay money to get computertime on the grid. This way companies can have access to a virtual supercomputer for a relatively small amount of money, and just for the time they need it.
Security
An important subject of grids architecture is their security. PC's running calculations should be sufficiently secured against illegal use by third parties. Also, data that is sent through the grid should not be altered and the grid infrastructure must be sure the PC's calculate their tasks as expected. Much work in this field must be done, as grids are a relatively new technology.
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