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Tightly-coupled multiprocessor

Short answer

Processors share a common memory and I/O through an interconnection network; each may have a cache. Communication is fast via shared memory, but memory contention and cache coherence limit scalability.

Discuss tightly-coupled multiprocessors with block diagram.

A tightly coupled multiprocessor has several processors that share a common global memory and I/O channels and are controlled by one operating system. Processors communicate through the shared memory, so the data rate is high and the delay is low.

  +-------+  +-------+       +-------+
  | CPU 1 |  | CPU 2 |  ...  | CPU n |
  +-------+  +-------+       +-------+
  | cache |  | cache |       | cache |
  +---+---+  +---+---+       +---+---+
      |          |               |
  ==============================================
        Interconnection network (bus / crossbar /
        multistage / multiport memory)
  ==============================================
      |            |             |
  +---v---+    +---v---+     +---v---+
  |Memory |    |Memory |     |  I/O  |
  |  M1   | ...|  Mk   |     | chan. |
  +-------+    +-------+     +-------+
  • Each processor may have a local cache or memory to cut bus traffic, and the shared memory is made up of several modules.
  • Processors, shared memory and I/O are connected by a common bus, crossbar switch or multiport memory.
  • Merits: fast interprocessor communication, simple programming model, high data rate.
  • Demerits: memory contention and bus bottleneck, cache coherence problems, poor scalability.

✓ Answer checked by Claude Opus 5.5 (high effort)

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