Some computer organizations and their effectiveness

  • Authors:
  • Michael J. Flynn

  • Affiliations:
  • Department of Computer Science, The Johns Hopkins University, Baltimore, MD

  • Venue:
  • IEEE Transactions on Computers
  • Year:
  • 1972

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Abstract

A hierarchical model of computer organizations is developed, based on a tree model using request/service type resources as nodes. Two aspects of the model are distinguished: logical and physical. General parallel- or multiple-stream organizations are examined as to type and effectiveness--especially regarding intrinsic logical difficulties. The overlapped simplex processor (SISD) is limited by data dependencies. Branching has a particularly degenerative effect. The parallel processors [single-instruction stream-multipledata stream (SIMD)] are analyzed. In particular, a nesting type explanation is offered for Minsky's conjecture--the performance of a parallel processor increases as log M instead of M (the number of data stream processors). Multiprocessors (MIMD) are subjected to a saturation syndrome based on general communications lockout. Simplified queuing models indicate that saturation develops when the fraction of task time spent locked out (L/E) approaches 1/n, where n is the number of processors. Resources sharing in multiprocessors can be used to avoid several other classic organizational problems.