II. INPUT HARDWARE

Input hardware consists of external devices—that is, components outside of the computer’s CPU—that provide information and instructions to the computer. A light pen is a stylus with a light-sensitive tip that is used to draw directly on a computer’s video screen or to select information on the screen by pressing a clip in the light pen or by pressing the light pen against the surface of the screen. The pen contains light sensors that identify which portion of the screen it is passed over.

A mouse is a pointing device designed to be gripped by one hand. It has a detection device (usually a ball, a light-emitting diode [LED], or a low-powered laser) on the bottom that enables the user to control the motion of an on-screen pointer, or cursor, by moving the mouse on a flat surface. As the device moves across the surface, the cursor moves across the screen. To select items or choose commands on the screen, the user presses a button on the mouse. A joystick is a pointing device composed of a lever that moves in multiple directions to navigate a cursor or other graphical object on a computer screen.

A keyboard is a typewriter-like device that allows the user to type in text and commands to the computer. Some keyboards have special function keys or integrated pointing devices, such as a trackball or touch-sensitive regions that let the user’s finger motions move an on-screen cursor.

Touch-screen displays, which are video displays with a special touch-sensitive surface, are also becoming popular with personal electronic devices—examples include the Apple iPhone and Nintendo DS video game system. Touch-screen displays are also becoming common in everyday use. Examples include ticket kiosks in airports and automated teller machines (ATM).

An optical scanner uses light-sensing equipment to convert images such as a picture or text into electronic signals that can be manipulated by a computer. For example, a photograph can be scanned into a computer and then included in a text document created on that computer. The two most common scanner types are the flatbed scanner, which is similar to an office photocopier, and the handheld scanner, which is passed manually across the image to be processed.

A microphone is a device for converting sound into signals that can then be stored, manipulated, and played back by the computer. A voice recognition module is a device that converts spoken words into information that the computer can recognize and process.

A modem, which stands for modulator-demodulator, is a device that connects a computer to a telephone line or cable television network and allows information to be transmitted to or received from another computer. Each computer that sends or receives information must be connected to a modem. The digital signal sent from one computer is converted by the modem into an analog signal, which is then transmitted by telephone lines or television cables to the receiving modem, which converts the signal back into a digital signal that the receiving computer can understand.

A network interface card (NIC) allows the computer to access a local area network (LAN) through either a specialized cable similar to a telephone line or through a wireless (Wi-Fi) connection. The vast majority of LANs connect through the Ethernet standard, which was introduced in 1983.