The Essentials ofComputer(computer) 454

The Essentials ofComputer(computer) 454 - Shared memory...

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Shared memory MIMD machines can be divided into two categories accord- ing to how they synchronize their memory operations. In Uniform Memory Access ( UMA ) systems, all memory accesses take the same amount of time. A UMA machine has one pool of shared memory that is connected to a group of processors through a bus or switch network. All processors have equal access to memory, according to the established protocol of the interconnection network. As the number of processors increases, a switched interconnection network (requir- ing 2 n connections) quickly becomes very expensive in a UMA machine. Bus- based UMA systems saturate when the bandwidth of the bus becomes insufficient for the number of processors in the system. Multistage networks run into wiring constraints and significant latency if the number of processors becomes very large. Thus the scalability of UMA machines is limited by the properties of inter- connection networks. Symmetric multiprocessors are well-known UMA architec- tures. Specific examples of UMA machines include Sun’s Ultra Enterprise,
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