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Limitations of single bus system

Short answer

A single bus limits bandwidth because only one transfer occurs at a time, causing slow devices to delay fast ones. Its length and load increase propagation delay. Arbitration adds overhead, and a bus failure stops the whole system, so scalability is limited.

Discuss the limitations of using a single bus system to connect different devices in any given system.

A single bus connects the CPU, memory and all I/O devices to one shared set of lines. It is simple and cheap, but it has these limitations:

  1. Bandwidth bottleneck: only one transfer can happen at a time. When many devices compete, they must wait, and overall speed falls.
  2. Speed mismatch: fast devices (CPU, memory) must share the bus with slow devices (keyboard, printer), so the bus is held up by the slowest devices.
  3. Propagation delay: as more devices are attached, the bus gets longer and has more capacitive load, so signals take longer and the clock must be slower.
  4. Arbitration overhead: the bus must be granted to one device for every transfer, which adds delay and needs extra control hardware.
  5. Single point of failure: if the bus fails, the whole system stops.
  6. Limited scalability: beyond a certain point, adding devices reduces performance instead of improving it.

These problems are reduced by using a bus hierarchy with separate local, system and expansion buses joined by bridges.

✓ Answer checked by Claude Opus 5.5 (high effort)

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