Which of the following is NOT classified as a peripheral?

In the context of computer hardware, peripherals are typically defined as external devices that provide input and output functions to a computer system. These devices connect to the computer, allowing users to interact with it and for the computer to output information to users.

A hard drive is classified as a primary storage device rather than a peripheral because it is an integral part of the computer's internal architecture, responsible for the long-term storage of data. It typically connects via internal interfaces such as SATA (Serial Advanced Technology Attachment) or NVMe (Non-Volatile Memory Express), making it a core component of the computer system.

On the other hand, a mouse, keyboard, and monitor serve as peripherals. They connect externally to the computer: the mouse and keyboard are input devices that allow users to enter data and commands, while the monitor acts as an output device that displays information visually. This distinction helps clarify the role of each device within the overall functioning of a computer system.