Which of the following is NOT considered a peripheral device?

The motherboard is not considered a peripheral device because it is a fundamental component of a computer system that connects all other hardware. It acts as the main circuit board and is essential for the operation of the computer. It houses the CPU, memory, and provides connectors for other components, including peripherals.

In contrast, peripherals are external devices that connect to the computer and enhance its functionality, but they are not necessary for the computer to operate. A monitor is needed to display output, a keyboard is essential for input, and an external hard drive provides additional storage, all of which fall under the category of peripheral devices.