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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
Uniform: All processors take the same time to reach all memory locations.
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
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
This simple two level memory access model gets more complicated in proposed 10 year out "petaflop" designs

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