In a computer system, what is the system unit?

The system unit refers to the main chassis of a computer that houses the essential components required for its operation. This includes vital parts such as the central processing unit (CPU), motherboard, memory (RAM), storage drives (HDD or SSD), and power supply. The system unit serves as the central hub of a computer where all primary activities occur, enabling the interaction between hardware and software.

The other options represent peripheral devices or components that are important for input and output functionality but do not contain the core system hardware. The keyboard is an input device that allows users to interact with the computer, the monitor is an output device that displays information to the user, and the printer is another output device used for producing physical copies of digital documents. None of these serve as the main chassis, which is fundamentally what the system unit encompasses.