A computer is an electronic device that stores, retrieves, and processes data, and can be programmed with instructions. A computer is composed of hardware and software, and can exist in a variety of sizes and configurations. Hardware is the physical equipment of a computer system, including the central processing unit (CPU), data-storage devices, terminals, printer, etc. Software is a program or set of instructions or rules that control the operation of a computer. The most obvious hardware component is the computer case. The case is where size comes into play. A bigger case allows more room for components. A bigger case is most often used for servers. For basic home computing needs, a small or mid-sized case is most common. Cases also come in many colors mainly for user preference. The most important component for a bare bones PC is the motherboard, a printed circuit board where the processing components are connected. The motherboard itself is just a piece of fiberglass. It's actually the hardware mounted on it that does all the work in the computer. The motherboard connects directly or indirectly to every other part of the computer. IT is the "heart" of your PC. It handles the CPU and all system memory. It accepts expansion devices such as sound and network cards, and modems. Without the motherboard everything is useless. The motherboard receives its power from the power supply. The power supply is the metal box usually found in a corner of the case. The power supply is visible from the back of many systems because it contains the power-cord receptacle and the cooling fan. This is what tells the PC to turn on or off. The cooling fan that is found at the power supply is used for cooling purposes. It draws cooler air into the case from the outside, expels warm air from inside, or moves air across a heatsink to cool a particular component. Another very