Which components are commonly connected by the data bus?

Concept

A system data bus carries binary payloads—such as instruction words, operands, and results—between major functional units. It is distinct from the address bus, which identifies a location or device, and the control bus, which carries commands and timing signals.

A component belongs on the system data path when it must send or receive these payloads during normal fetch, read, write, or input/output transfers.

Application

1. During an instruction fetch, the CPU requests a memory location and memory returns the instruction word to the CPU over the data bus.

2. During a memory read or write, operands and results move between the CPU and memory over the data bus.

3. During an I/O transfer, data moves between the CPU or memory and an I/O interface over the same system data path.

Cross-check and contrast

• Memory and cache describe only part of the memory hierarchy; cache fills and write-backs do not name every major endpoint of the system data bus.

• A clock generator supplies periodic timing pulses on clock lines rather than instruction or operand payloads.

• The ALU and control unit are internal CPU subunits and communicate through internal processor interconnections.

• CPU, memory, and I/O devices collectively cover the major producers and consumers of system data.

Therefore, the components commonly connected by the data bus are CPU, memory, and I/O devices.