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In computer science, distributed shared memory (DSM) 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 "shared" essentially means that the address space is shared (same physical address on two processors refers to the same location in memory). Distributed global address space (DGAS), is a similar term for a wide class of software and hardware implementations, in which each node of a cluster has access to shared memory in addition to each node's non-shared private memory. A distributed-memory system (often called a multicomputer) consist of multiple independent processing nodes with local memory modules which is connected by a general interconnection network. Software DSM systems can be implemented in an operating system, or as a programming library and can be thought of as extensions of the underlying virtual memory architecture. When implemented in the operating system, 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. A distributed shared memory system implements the shared-memory model on a physically distributed memory system. ==Software DSM implementation== There are three ways of implementing a software distributed shared memory: * page based approach using the system’s virtual memory; * shared variable approach using some routines to access shared variables; * object based approach ideally accessing shared data through object-oriented discipline. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Distributed shared memory」の詳細全文を読む スポンサード リンク
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