Which component is primarily responsible for data storage in a computer system?

The hard drive is primarily responsible for data storage in a computer system. It is a non-volatile storage medium that holds data permanently, even when the computer is turned off. This allows users to store a variety of data, including the operating system, applications, and personal files, ensuring that information is retained between sessions.

In contrast, while RAM (Random Access Memory) serves as the system's short-term memory and is crucial for temporarily holding data and instructions currently in use, it is volatile and does not store data permanently. Cache memory acts as a small, high-speed storage located close to the CPU to speed up access to frequently used data, but it does not store information long-term either. The CPU (Central Processing Unit) is responsible for processing instructions and performing calculations rather than storing data, thus it also does not serve as a primary data storage component.

This distinction highlights why the hard drive is the correct answer, as it fulfills the critical role of long-term data storage in a computer system.