What is the definition of a CPU?

The correct answer is the definition of the CPU, which stands for Central Processing Unit. It is often referred to as the brain of the computer because its primary role is to perform data processing. This includes executing instructions from programs, performing calculations, and managing data flow between other components. The CPU interprets and processes data, making it essential for all computing tasks.

Other options describe different parts of a computer but do not reflect the specific function of the CPU. The physical computer case refers to the enclosure that houses all components, while the internal hard drive is dedicated to storage. The part of the computer that stores and manages memory relates to components like RAM or memory management units, differentiating their functions from that of the CPU. Therefore, option C accurately defines the CPU's role in the computer system.