Which device is used to store data on a computer?

The hard drive is the primary device used to store data on a computer. It functions as a long-term storage solution, allowing users to save files, applications, and the operating system itself. The hard drive retains this information even when the computer is powered off, making it essential for data storage and retrieval.

In contrast, monitors and printers serve different purposes; the monitor is used for displaying output visually, while the printer produces physical copies of digital documents. The mouse is an input device that allows users to interact with the computer, but it does not store data. Thus, the hard drive clearly stands out as the correct answer because of its specific function as a data storage medium.