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Uniform: All processors take the same time to reach all memory locations.
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Nonuniform (NUMA): Memory access is not uniform so that it takes a different time to get data by a given processor from each memory bank. This is natural for distributed memory machines but also true in most modern shared memory machines
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DASH (Hennessey at Stanford) is best known example of such a virtual shared memory machine which is logicall shared but physically distributed.
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ALEWIFE from MIT is a similar project
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TERA (from Burton Smith) is Uniform memory access logically shared memory machine
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Most NUMA machines these days have two memory access times
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Local memory (divided in registers caches etc) and
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Nonlocal memory with little or no difference in access time for different nonlocal memories
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