HTML version of Scripted Foils prepared 11 November 1996

Foil 11 The GRAPE N-Body Machine

From CPS615-Lecture on Computer Architectures and Networks Delivered Lectures of CPS615 Basic Simulation Track for Computational Science -- 12 September 96. by Geoffrey C. Fox *
Secs 237.6
1 N body problems (e.g. Newton's laws for one million stars in a globular cluster) can have succesful special purpose devices
2 See GRAPE (GRAvity PipE) machine (Sugimoto et al. Nature 345 page 90,1990)
  • Essential reason is that such problems need much less memory per floating point unit than most problems
  • Globular Cluster: 10^6 computations per datum stored
  • Finite Element Iteration: A few computations per datum stored
  • Rule of thumb is that one needs one gigabyte of memory per gigaflop of computation in general problems and this general design puts most cost into memory not into CPU.
3 Note GRAPE uses EXACTLY same parallel algorithm that one finds in the books (e.g. Solving Problems on Concurrent Processors) for N-body problems on classic distributed memory MIMD machines
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