What is the main component of a system unit?

The main component of a system unit is the motherboard, which serves as the central circuit board that connects and communicates between various hardware components within a computer. It provides the foundational platform for CPU, memory, storage, and various peripherals to interface with one another.

The motherboard houses the CPU, RAM, and other essential components, and it includes slots for expansion cards like the graphics card. Its importance cannot be overstated, as it directs data and power to different parts of the computer and facilitates communication among them.

While other components like the power supply, CPU fan, and graphics card are crucial for the functionality of a computer, they do not serve the central role that the motherboard does. The power supply provides electrical power, the CPU fan helps in cooling the processor, and the graphics card handles rendering images, but none of these function independently without the motherboard coordinating their operations. Therefore, the motherboard stands out as the principal component within a system unit, making it the correct answer.