Distributed memory

Distributed memory
An illustration of a distributed memory system of three computers

In computer science, distributed memory refers to a multiple-processor computer system in which each processor has its own private memory. Computational tasks can only operate on local data, and if remote data is required, the computational task must communicate with one or more remote processors. In contrast, a shared memory multi processor offers a single memory space used by all processors. Processors do not have to be aware where data resides, except that there may be performance penalties, and that race conditions are to be avoided.



In a distributed memory system there is typically a processor, a memory, and some form of interconnection that allows programs on each processor to interact with each other. The interconnect can be organised with point to point links or separate hardware can provide a switching network. The network topology is a key factor in determining how the multi-processor machine scales. The links between nodes can be implemented using some standard network protocol (for example Ethernet), using bespoke network links (used in for example the Transputer), or using dual ported memories.

Programming distributed memory machines

The key issue in programming distributed memory systems is how to distribute the data over the memories. Depending on the problem solved, the data can be distributed statically, or it can be moved through the nodes. Data can be moved on demand, or data can be pushed to the new nodes in advance.

As an example, if a problem can be described as a pipeline where data X is processed subsequently through functions F, G, H, etc. (the result is H(G(F(X)))), then this can be expressed as a distributed memory problem where the data is transmitted first to the node that performs F that passes the result onto the second node that computes G, and finally to the third node that computes H. This is also known as systolic computation.

Data can be kept statically in nodes if most computations happen locally, and only changes on edges have to be reported to other nodes. An example of this is simulation where data is modeled using a grid, and each node simulates a small part of the larger grid. On every iteration, nodes inform all neighboring nodes of the new edge data.

Distributed shared memory

Similarly, in distributed shared memory each node of a cluster has access to a large shared memory in addition to each node's limited non-shared private memory.

Shared memory versus distributed memory versus distributed shared memory

The advantage of (distributed) shared memory is that it offers a unified address space in which all data can be found.

The advantage of distributed memory is that it excludes race conditions, and that it forces the programmer to think about data distribution.

The advantage of distributed (shared) memory is that it is easier to design a machine that scales with the algorithm

Distributed shared memory hides the mechanism of communication - it does not hide the latency of communication.

Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Distributed Memory —   [dt. »verteilter Speicher«], Aufteilung des Arbeitsspeichers bei einem Parallelrechner. Bei diesem Konzept verfügt jeder Prozessor über einen eigenen Arbeitsspeicher, den er unabhängig von den anderen Prozessoren benutzt. Das Gegenteil des… …   Universal-Lexikon

  • distributed memory — paskirstytoji atmintis statusas T sritis informatika apibrėžtis Atmintis, paskirstyta į sritis, kurių kiekviena paskirta kuriam nors iš lygiagrečiai veikiančių procesorių. atitikmenys: angl. distributed memory ryšiai: dar žiūrėk – lygiagretusis… …   Enciklopedinis kompiuterijos žodynas

  • Distributed computing — is a field of computer science that studies distributed systems. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal …   Wikipedia

  • Distributed shared memory — (DSM), in Computer Architecture is a form of memory architecture where the (physically separate) memories can be addressed as one (logically shared) address space. Here, the term shared does not mean that there is a single centralized memory but… …   Wikipedia

  • Distributed Shared Memory — (verteilter gemeinsamer Speicher, DSM) ist ein Ausdruck aus der Informatik und bezieht sich auf die Verteilung des Arbeitsspeichers von Computerclustern. Da sich die einzelnen CPUs nicht auf einem gemeinsamen Mainboard befinden, existiert auch… …   Deutsch Wikipedia

  • Memory virtualization — In computer science, memory virtualization decouples volatile random access memory (RAM) resources from individual systems in the data center, and then aggregates those resources into a virtualized memory pool available to any computer in the… …   Wikipedia

  • Distributed hash table — A distributed hash table (DHT) is a class of a decentralized distributed system that provides a lookup service similar to a hash table; (key, value) pairs are stored in a DHT, and any participating node can efficiently retrieve the value… …   Wikipedia

  • Distributed GIS — concerns itself with GI Systems that do not have all of the system components in the same physical location. This could be the processing, the database, the rendering or the user interface. Examples of distributed systems are web based GIS,… …   Wikipedia

  • Distributed learning — may refer to distance education . Distributed learning is defined as opposed to massed learning.[1] Reviews of material separated by a long period of time ( spaced ) yield more learning than reviews separated by a shorter period of time ( massed… …   Wikipedia

  • Memory coherence — is an issue that affects the design of computer systems in which two or more processors or cores share a common area of memory.[1][2][3][4] In a uniprocessor system (whereby, in today s terms, there exists only one core), there is only one… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”