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System Characteristics

Network Characteristics

• Interconnect
  • Topology: schematic layout of connections

  • Dedicated connections

  • Shared connection medium

• Routing: the path taken by data from source to destination, on modern systems often transparent to the user, eg. VCR Vitrual Channel Routing

• Bandwidth: the amount of data a network can pass from one point to another. This is usually expressed in Mb/sec (Megabytes per seconds)

• Latency: the time delay between starting to send data to another point in the network and the data arriving at that point. Usually expressed in ms (microseconds)

Architecture Characteristics

• Shared Memory
  • multiple processors access a central memory

  • bus configuration limits the number of processors, upper limit circa 20 - high latency due to bus conflicts, high bandwidth

  • switch configuration on a large system can result in very complex wiring and a bottleneck at the switch (hierarchical switches) - possible improved latency at a cost of reduced bandwidth

• Distributed Memory
  • processors connected in a network each with local memory, bandwidth scales with number of processors

  • latency grows with the number of processors

  • VSM - Virtual Shared Memory - emulated SM on a DM system

Architecture Details

Do I need to know?

• In matching the solution to the machine to optimise performance (exploiting the machines strengths and avoiding its weaknesses) the choice of solution/algorithm can be very important

• What is relevant?
  • memory organisation - where data is located

  • memory available on each processor - MIMD DM

  • interconnections - ease of communications

  • interconnection performance characteristics