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Foil 16 Types of Parallel Memory Architectures -- Physical Characteristics

From CPS615-Lecture on Performance(end) and Computer Technologies(start) Delivered Lectures of CPS615 Basic Simulation Track for Computational Science -- 10 September 96. by Geoffrey C. Fox *
Secs 486.7
1 Uniform: All processors take the same time to reach all memory locations.
2 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
  • DASH (Hennessey at Stanford) is best known example of such a virtual shared memory machine which is logically shared but physically distributed.
  • ALEWIFE from MIT is a similar project
  • TERA (from Burton Smith) is Uniform memory access and logically shared memory machine
3 Most NUMA machines these days have two memory access times
  • Local memory (divided in registers caches etc) and
  • Nonlocal memory with little or no difference in access time for different nonlocal memories
4 This simple two level memory access model gets more complicated in proposed 10 year out "petaflop" designs
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