Distributed computing Concurrency

Distributed computing implements a kind of concurrency. It interrelates tightly with concurrent programming so much that they are sometimes not taught as distinct subjects [3].

[edit] Multiprocessor systems

A multiprocessor system is simply a computer that has more than one CPU on its motherboard. If the operating system is built to take advantage of this, it can run different processes (or different threads belonging to the same process) on different CPUs.

[edit] Multicore systems

Intel CPUs from the late Pentium 4 era (Northwood and Prescott cores) employed a technology called Hyperthreading that allowed more than one thread (usually two) to run on the same CPU. The more recent Sun UltraSPARC T1, AMD Athlon 64 X2, AMD Athlon FX, AMD Opteron, Intel Pentium D, Intel Core, Intel Core 2 and Intel Xeon processors feature multiple processor cores to also increase the number of concurrent threads they can run.

[edit] Multicomputer systems

A multicomputer may be considered to be either a loosely coupled NUMA computer or a tightly coupled cluster. Multicomputers are commonly used when strong compute power is required in an environment with restricted physical space or electrical power.

Common suppliers include Mercury Computer Systems, CSPI, and SKY Computers.

Common uses include 3D medical imaging devices and mobile radar.

[edit] Computing taxonomies

The types of distributed systems are based on Flynn's taxonomy of systems; single instruction, single data (SISD), single instruction, multiple data (SIMD), multiple instruction, single data (MISD), and multiple instruction, multiple data (MIMD). Other taxonomies and architectures available at Computer architecture and in Category:Computer architecture.

[edit] Computer clusters

Main article: Cluster computing

A cluster consists of multiple stand-alone machines acting in parallel across a local high speed network. Distributed computing differs from cluster computing in that computers in a distributed computing environment are typically not exclusively running "group" tasks, whereas clustered computers are usually much more tightly coupled. Distributed computing also often consists of machines which are widely separated geographically.

[edit] Grid computing

Main article: Grid computing

A grid uses the resources of many separate computers, loosely connected by a network (usually the Internet), to solve large-scale computation problems. Public grids may use idle time on many thousands of computers throughout the world. Such arrangements permit handling of data that would otherwise require the power of expensive supercomputers or would have been impossible to analyze.

[edit] Languages

Nearly any programming language that has access to the full hardware of the system could handle distributed programming given enough time and code. Remote procedure calls distribute operating system commands over a network connection. Systems like CORBA, Microsoft DCOM, Java RMI and others, try to map object oriented design to the network. Loosely coupled systems communicate through intermediate documents that are typically human readable (e.g. XML, HTML, SGML, X.500, and EDI).

[edit] Examples

[edit] Projects

Main article: List of distributed computing projects

A variety of distributed computing projects have grown up in recent years. Many are run on a volunteer basis, and involve users donating their unused computational power to work on interesting computational problems. Examples of such projects include the Stanford University Chemistry Department Folding@home project, which is focused on simulations of protein folding to find disease cures and to understand biophysical systems; World Community Grid, an effort to create the world's largest public computing grid to tackle scientific research projects that benefit humanity, run and funded by IBM; SETI@home, which is focused on analyzing radio-telescope data to find evidence of intelligent signals from space, hosted by the Space Sciences Laboratory at the University of California, Berkeley; and distributed.net, which is focused on breaking various cryptographic ciphers.[4]

Distributed computing projects also often involve competition with other distributed systems. This competition may be for prestige, or it may be a matter of enticing users to donate processing power to a specific project. For example, stat races are a measure of the work a distributed computing project has been able to compute over the past day or week. This has been found to be so important in practice that virtually all distributed computing projects offer online statistical analyses of their performances, updated at least daily if not in real-time.