Internal hardware components of a computer revision notes

Core components

A computer system contains several internal components that must communicate. The processor performs processing, while main memory stores data and instructions that the processor needs. I/O controllers provide control of communication with input and output devices. The processor, main memory and I/O controllers are connected by buses.

Buses and communication

A bus is a set of parallel communication pathways used to transfer information between components. The address bus carries the address of a memory location or an input/output location. The data bus carries the data being transferred. The control bus carries control signals that coordinate the operation, such as indicating the type or direction of a transfer. These buses work together: an address identifies the location, data carries the value, and control signals help the receiving component interpret the transfer.

For example, when the processor needs information from main memory, it places the required address on the address bus. A control signal indicates the required operation, and the relevant value is transferred on the data bus. Communication is necessary because the processor, memory and I/O controllers are separate components with different roles; buses provide a structured way for them to exchange addresses, data and control information.

Addressable memory

Memory is addressable when each memory location has its own address. The processor can identify a particular location by placing its address on the address bus. The address is not the stored data itself: it identifies where the data can be found.

Architectures

In a von Neumann architecture, instructions and data use the same memory and communication pathway. This architecture is used extensively in general-purpose computing systems. In a Harvard architecture, instructions and data use separate memory and communication pathways. Harvard architecture processors are used extensively in embedded systems such as digital signal processing (DSP) systems.

Common errors

Do not confuse a bus with a single component: it is a communication pathway or set of pathways. Do not say that the address bus carries the data value; the data bus carries data. Do not treat the control bus as an address bus. Also, do not describe von Neumann and Harvard architectures merely as different processor types: the important distinction is how instructions and data are stored and communicated. Finally, remember that a memory address identifies a location, whereas the data bus transfers the contents or value involved in the communication.