Shared memory

In computer science, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Shared memory is an efficient means of passing data between programs. Depending on context, programs may run on a single processor or on multiple separate processors.

Using memory for communication inside a single program, e.g. among its multiple threads, is also referred to as shared memory.

In computer hardware, shared memory refers to a (typically large) block of random access memory (RAM) that can be accessed by several different central processing units (CPUs) in a multiprocessor computer system.

Shared memory systems may use:

A shared memory system is relatively easy to program since all processors share a single view of data and the communication between processors can be as fast as memory accesses to a same location. The issue with shared memory systems is that many CPUs need fast access to memory and will likely cache memory, which has two complications:

Technologies like crossbar switches, Omega networks, HyperTransport or front-side bus can be used to dampen the bottleneck-effects.

In case of a Heterogeneous System Architecture (processor architecture that integrates different types of processors, such as CPUs and GPUs, with shared memory), the memory management unit (MMU) of the CPU and the input–output memory management unit (IOMMU) of the GPU have to share certain characteristics, like a common address space.

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