Distributed Shared Memory (DSM), in computer science, refers to a wide class of software and hardware implementations, in which each node of a cluster has access to a large shared memory in addition to each node's limited non-shared private memory. Computer science is the study of information and computation. ... A node is a device connected to a computer network. ... Linux Cluster at Purdue University A computer cluster is a group of loosely coupled computers that work together closely so that in many respects it can be viewed as though it were a single computer. ...

Software DSM systems can be implemented within an operating system, or as a programming library. Software DSM systems implemented in the operating system can be thought of as extensions of the underlying virtual memory architecture. Such systems are transparent to the developer; which means that the underlying distributed memory is completely hidden from the users. In contrast, Software DSM systems implemented at the library or language level are not transparent and developers usually have to program differently. However, these systems offer a more portable approach to DSM system implementation.

Software DSM systems also have the flexibility to organise the shared memory region in different ways. The page based approach organises shared memory into pages of fixed size. In contrast, the object based approach organises the shared memory region as an abstract space for storing sharable objects of variable sizes.

Shared memory architecture may involve separating memory into shared parts distributed amongst nodes and main memory; or distributing all memory between nodes. A coherence protocol, chosen in accordance with a consistency model, maintains memory coherence. Shared memory refers to a (typically) large block of Random access memory that can be accessed by several different central processing units (CPUs) in a multiple-processor computer system. ... In computer science, a coherence protocol is a protocol in systems with distributed memory (distributed shared memory systems, including multiprocessors), which maintains memory coherence according to specified consistency model. ... In computer science, in a distributed system such as a distributed shared memory system or a distributed data store such as a database, filesystem, or web caching system, there are a number of possible data consistency models. ... Memory coherence (also cache coherence or cache consistency) is the property of the shared memory systems (multiprocessors and distributed shared memory systems) in which any shared piece of memory (cache line or memory page) gives consistent values with accordance to earlier agreed consistency model despite accesses (maybe parallel) from different...

Examples of such systems include:

• Delphi
• JIAJIA
• Kerrighed
• NanosDSM
• Strings
• TreadMarks

Kerrighed is a single-system image (SSI) cluster software for Linux. ... TreadMarks is a distributed shared memory system created at Rice University. ...

External links

• JIAJIA - A Software DSM System