The function of a system bus in computer architecture is to facilitate communication between various components of a computer, such as the CPU, memory, and input/output devices. It consists of a set of wires and protocols that carry data, addresses, and control signals among these components. The bus architecture allows for a unified pathway to reduce complexity and improve the efficiency of data transfer. By using a system bus, the architecture can be more modular, making it easier for components to communicate without needing direct connections.