The System Unit

Whether you are a home user or a business user, you most likely will purchase a new computer or upgrade an existing computer at some time in the future. Thus, you should understand the purpose of each component in a computer. A computer includes devices used for input, processing, output, storage, and communications. Many of these components are part of the system unit.

 The system unit is a case that contains electronic components of the computer used to process data. System units are available in a variety of shapes and sizes. The case of the system unit, sometimes called the chassis, is made of metal or plastic and protects the internal electronic components from damage. All computers and mobile devices have a system unit.

 On desktop personal computers, the electronic components and most storage devices are part of the system unit. Other devices, such as the keyboard, mouse, microphone, monitor, printer, USB flash drive, scanner, Web cam, and speakers, normally occupy space outside the system unit. An all-in-one desktop personal computer is an exception, which houses the monitor and the system unit in the same case. The trend is toward a smaller form factor, or size and shape, of the desktop personal computer system unit.

 On most notebook computers, including netbooks, the keyboard and pointing device often occupy the area on the top of the system unit, and the display attaches to the system unit by hinges. The location of the system unit on a Tablet PC varies, depending on the design of the Tablet PC. With the slate Tablet PC, which typically does not include a keyboard, the system unit is behind the display. On a convertible Tablet PC, by contrast, the system unit is positioned below a keyboard, providing functionality similar to a traditional notebook computer or netbook. The difference is the display attaches to the system unit with a swivel-type hinge, which enables a user to rotate the display and fold it down over the keyboard to look like a slate Tablet PC. The system unit on an Ultra-Mobile PC, a smart phone, and a PDA usually consumes the entire device. On these mobile computers and devices, the display often is built into the system unit.

 With game consoles, the input and output devices, such as controllers and television, reside outside the system unit. On handheld game consoles, portable media players, and digital cameras, by contrast, the packaging around the system unit houses the input devices and display.

 At some point, you might have to open the system unit on a desktop personal computer to replace or install a new electronic component. For this reason, you should be familiar with the electronic components of a system unit. Some of these components include the processor, memory, adapter cards, drive bays, and the power supply.

 The processor interprets and carries out the basic instructions that operate a computer. Memory typically holds data waiting to be executed. The electronic components and circuitry of the system unit, such as the processor and memory, usually are part of or are connected to a circuit board called the motherboard. Many current motherboards also integrate sound, video, and networking capabilities.

 Adapter cards are circuit boards that provide connections and functions not built into the motherboard or expand on the capability of features integrated into the motherboard. For example, a sound card and a video card are two types of adapter cards found in some desktop personal computers today.

 Devices outside the system unit often attach to ports on the system unit by a connector on a cable. These devices may include a keyboard, mouse, microphone, monitor, printer, scanner, USB flash drive, card reader/writer, Web cam, and speakers. A drive bay holds one or more disk drives. The power supply converts electricity from a power cord plugged in a wall outlet into a form that can be used by the computer.

The Motherboard

 The motherboard, sometimes called a system board, is the main circuit board of the system unit. Many electronic components attach to the motherboard; others are built into it.

 A computer chip is a small piece of semi-conducting material, usually silicon, on which integrated circuits are etched. An integrated circuit contains many microscopic pathways capable of carrying electrical current. Each integrated circuit can contain millions of elements such as resistors, capacitors, and transistors. A transistor, for example, can act as an electronic switch that opens or closes the circuit for electrical charges. Today's computer chips contain millions or billions of transistors. Most chips are in bigger than one-half-inch square. Manufacturers package chips so that the chips can be attached to a circuit board such as a motherboard or an adapter card.