Computers work through an interaction of hardware and software. Hardware refers to the parts of a computer that you can see and touch, including the case and everything inside it. The most important piece of hardware is a tiny rectangular chip inside your computer called the central processing unit (CPU), or microprocessor. It's the "brain" of your computer the part that translates instructions and performs calculations. Hardware items such as your monitor, keyboard, mouse, printer, and other items are often called hardware devices, or devices.