Define a "clean" model for machine architecture
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Memory hierarchy including caches and geomterical (distributed) effects
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Define a low level "Program Execution Model" (PEM) which allows one to describe movement of information and computation in the machine
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This can be thought of as "MPI"/assembly language of the machine
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On top of low level PEM, one can build an hierarchical (layered) software model
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At the top of this layered software model, one finds objects or Problem Solving Environments (PSE's)
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At an intermediate level there is Parallel C C++ or Fortran
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One can program at each layer of the software and augment it by "escaping" to a lower level to improve performance
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Directives (HPF assertions) and explicit insertion of lower level code (HPF extrinsics) are possible
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