Skip to main content

Bus structure of a typical computer

Short answer

A typical system bus has address, data, and control lines connecting CPU, memory, and I/O. Single-bus designs are simple but slow; dual-bus separates memory and I/O for concurrency; a bus hierarchy with local, system, and expansion buses offers the best performance by matching bus speeds to device needs.

Compare and explain the bus structure of a typical computer system.

The bus structure of a typical computer uses a system bus that joins the CPU, main memory and I/O modules. It has three groups of lines.

 +-----+   +--------+   +--------+   +--------+
 | CPU |   | Memory |   | I/O 1  |   | I/O 2  |
 +--+--+   +---+----+   +---+----+   +---+----+
    |          |            |            |
 ===+==========+============+============+== Address bus
 ===+==========+============+============+== Data bus
 ===+==========+============+============+== Control bus
BusDirectionFunction
Address busOne way, CPU to othersSelects memory location or I/O port; width decides memory size
Data busTwo wayCarries data and instructions; width decides word moved per transfer
Control busBoth waysCarries Read/Write, interrupt, bus request/grant, clock, reset

Comparison of the common structures:

  • Single bus: all devices share one bus. Cheap and simple, but slow when busy.
  • Dual or multiple bus: a separate memory bus (CPU and memory) and I/O bus (peripherals). The CPU can use memory while I/O runs. Faster but costlier.
  • Bus hierarchy: local, system and expansion buses with bridges. Best performance and used in modern PCs.

Only one device drives the bus at one time, so arbitration is needed.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Computer Organization and Architecture chapter 1 questions →