Which component is known as the "brain" of a computer?

The CPU, or Central Processing Unit, is regarded as the "brain" of a computer because it performs the majority of the processing tasks. It interprets and executes instructions from programs, handling calculations and controlling other components of the computer to ensure they work together effectively. The CPU's ability to process data quickly and handle complex computations directly impacts the performance and efficiency of the entire system.

The motherboard, while crucial as the main circuit board that connects all components, does not actively process data; it facilitates communication between the CPU, memory, and other peripherals. Similarly, the hard drive serves as the storage device where data and programs are kept but does not engage in actual processing. Lastly, the power supply unit's role is to convert electrical power from an outlet into usable power for the computer’s components; it does not engage in processing tasks at all. Thus, the CPU stands out as the central figure in a computer’s operation, justifying its title as the "brain."