shared memory


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Related to shared memory: Message passing

shared memory

(1)
Memory in a parallel computer, usually RAM, which can be accessed by more than one processor, usually via a shared bus or network.

It usually takes longer for a processor to access shared memory than to access its own private memory because of contention for the processor-to-memory connections and because of other overheads associated with ensuring synchronised access. Computers using shared memory usually have some kind of local cache on each processor to reduce the number of accesses to shared memory. This requires a cache consistency protocol to ensure that one processor's cached copy of a shared memory location is invalidated when another processor writes to that location.

The alternative to shared memory is message passing where all memory is private to some particular processor and processors communicate by sending messages down special links. This is usually slower than shared memory but it avoids the problems of contention for memory and can be implemented more cheaply.

shared memory

(2)
Memory which can be access by more than one process in a multitasking operating system with memory protection. Some Unix variants, e.g. SunOS provide this kind of shared memory.

Unix manual pages: shmop(2), shmctl(2), shmget(2).

shared memory

(1) Using part of main memory to support a low-cost display circuit that does not have its own memory. See shared video memory.

(2) The common memory in a symmetric multiprocessing system that is available to all CPUs. See SMP.
References in periodicals archive ?
The calling process can access the shared memory on all processes.
Any processor can directly reference or access the shared memory at any position.
We also note for the record that this technique has proven effective in a shared memory environment [14] where the speedups were a factor of 29 on 32 processors of an SGI Origin 3000 system and a factor of 50 on 64 processors.
Section 2 describes the DSMP architecture and multigrain shared memory, and presents our performance metrics for DSMPs.
In some ways it is surprising that IBM has hung its hat on distributed shared memory so quickly, as evidenced by its $800m acquisition of Intel-based ccNUMA vendor Sequent Computer Systems Inc.
No longer do you need the budget of major government funded research facilities to afford supercomputers that because of their exceptionally large shared memory significantly reduce the time and effort required for research, simulation and modeling.
Model Distribution: If a model is too complex to be computed within the time step, RT-LAB allows the model to be distributed over several processors, automatically handling the inter-processor communication through TCP/IP, FireWire or Shared Memory.
This is not a problem in the shared-memory multiprocessor version if the MPI implementation is smart enough to take advantage of the shared memory.
Tera Computer Co is the latest supercomputer company to support the OpenMP application programming interface for shared memory programming, as part of bundled software available with its Tera MTA multi-threaded architecture systems.
Utilizing a scale-up, single-node architecture with breakthrough coherent shared memory, the appliance is being built to enable organizations to run enterprise resource planning (ERP), data warehouse, and other applications on a single, in-memory system and scale beyond 6TB.

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