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Classification

Flynn's Taxonomy

• Machines classified by instruction delivery mechanism and data stream

• A four character code is used
  • first 2 define instruction stream type

  • second 2 define data stream type

• Streams may be either single or multiple

• The possible variations are
  • SISD

  • SIMD

  • MISD

  • MIMD

Examples

• SISD: traditional Von Neuman architecture

• SIMD: original massively parallel machines
  • AMT DAP

  • MASPAR

  • Connection Machine

• MISD: data flow machine - experimental

• MIMD: flexible multi-processor of which there are 2 sub-classes
  • MIMD SM - Shared Memory

  • MIMD DM - Distributed Memory

SISD

Simple Diagrammatic Representation

SIMD

Simple Diagrammatic Representation

MIMD SM

Shared Memory

• All processors share the same main memory

• Relatively simple to program

• Direct use of multi-tasking techniques such as semaphores and Mutex

• All of the memory is accessible by every processor - small sections may be temporarily locked by one processor

• Examples
  • CRAY YMP, CRAY C90

  • IBM 3090

  • VAX 9000

  • Sequent Symmetry

Simple Diagrammatic Representation

MIMD DM

Distributed Memory

• Memory is distributed among the processors ie. each processor has its own memory - alternative acronym NUMA (Non Uniform Memory Access)

• Connectivity between processors is required
  • Bus or switch: potential bottleneck

  • all-to-all connections (increases with n2)

  • specialized topology (hard wired or using routing/switching processors)

  • networked workstations - usually a broadcast/multi-access medium such as
    • ethernet

    • ATM

    • UTP to hub

• Examples
  • Transputer based: Parsys, Meiko

  • DEC Alpha: Cray T3D

  • i860: Paragon, Delta, iPSC

  • SGI workstation cluster

Simple Diagrammatic Representation

Flynn's Taxonomy

An Analogy

• Consider the check-in desks at an airport
  • SISD: a single desk

  • SIMD: many desks and a supervisor with a megaphone issuing instructions which every desk obey

  • MIMD: many desks working at their own pace, synchronising via a central database