Web Summary

Keyboards: There are two categories of keyboards, devices that convert characters into electrical signals readable by the processor. The first is the traditional computer keyboard, which has all the keys of a typewriter plus some that are unique. The second category, specialty keyboards and terminals, includes three types of terminals: (1) A dumb terminal has screen and keyboard and can input and output but not process data. (2) An intelligent terminal has screen, keyboard, and its own processor and memory. One example is the automated teller machine (ATM), the self-service banking machine. Another is the point-of-sale (POS) terminal, used to record purchases in a store. (3) An Internet terminal provides access to the Internet. Examples are set-top boxes or Web terminals, stripped-down network computers, online game players, PC/TVs, and handheld wireless pocket PCsor personal digital assistants (PDAs).

Pointing Devices: Devices that control the cursor or pointer on a screen are pointing devices. They include the mouse and its variants, the touch screen, and various forms of pen input. (1) The mouse, which directs a pointer on the display screen, is moved on the desktop. Variants are the trackball, a movable ball mounted on a stationary device; the pointing stick, which protrudes from the keyboard; and the touchpad, a surface over which you move your finger. (2) The touch screen is a display screen that is sensitive to touch. (3) Devices for pen input include pen-based computer systems, in which users write with a penlike stylus on a screen; light pens, light-sensitive penlike devices; and digitizers, which convert drawings to digital data -- one example is the digitizing tablet.

Source Data-Entry Devices: Source-data entry devices create machine-readable data on magnetic media or paper or feed it directly into the computer's processor. As well as various scanning devices -- imaging systems, bar-code readers, mark- and character-recognition devices, and fax machines -- they include audio-input devices, video input, photographic input (digital cameras), voice-recognition systems, sensors, radio-frequency identification devices, and human-biology input devices. (1) Scanners use laser beams and reflected light to translate images of text, drawings, and photographs into digital form. One type is an imaging system , which converts text, drawings, and photos into digital form that can be processed or stored in a computer system. This has led to the new industry of electronic imaging, the integration of separate images using scanners. Another scanning device is the bar-code reader, which reads thezebra-striped bar codes on products to translate them into digital code. Magnetic-ink character recognition (MICR) reads check numbers; optical mark recognition (OMR) reads pencil marks; optical character recognition (OCR) reads preprinted characters, such as those on store price tags. The fax machine, the last type of scanner, reads images and sends them over phone lines. Dedicated fax machines only send and receive fax documents; fax modems are modems with fax capabilities. (2) Audio-input devices translate analog sounds (those with continuously variable waves) into digital 0s and 1s, either through audio boards or MIDI boards. (3) Webcams and video-input cards. A webcam is a camera attached to a computer to record moving images that can then be posted on a website in real time. Video-input cards translate analog film and videotape signals into digital form, using either frame-grabber video cards or full-motion video cards. (4) Digital cameras use light-sensitive processor chips to capture photographic images in digital form. (5) Voice-recognition systems convert speech into digital signals by comparing electrical patterns produced by voices with prerecorded patterns stored in a computer. (6) Sensors collect data directly from the environment and transmit it to a computer. (7) Radio-frequency identification(or RF-ID tagging)is based on an identifying tag bearing microchip that contains code numbers; these numbers are read by radio waves of a scanner linked to a database. (8) Human-biology input devices include biometric systems, which use biometrics, the study of body characteristics, to identify people through biological characteristics, and line-of-site systems, in which people point their eyes at a screen.

Softcopy: Softcopy refers to nonprinted data, such as that shown on a display screen. A display screen (monitor, screen) shows programming instructions and data as they are being input and information after it is processed. Screen clarity is affected by dot pitch, or space between pixels (the small units on screen that can be turned on or off); by resolution, which involves the number of pixels per square inch; and by refresh rate, the number of times per second pixels are recharged. Two types of monitors are CRT and flat-panel. A CRT (cathode-ray tube) is a vacuum tube. A flat-panel display consists of two plates of glass separated by a layer of a substance in which light is manipulated; one technology is liquid crystal display (LCD), in which molecules of liquid crystal create images by transmitting or blocking light. Flat-panel screens are either active-matrix display, in which each pixel on screen is controlled by its own transistor and so the image is brighter and sharper, or passive-matrix display, in which a transistor controls a row or column of pixels. Two common color and resolution standards for monitors are SVGA (the most common), which can produce 16 million possible colors, and XGA, which can produce 65,536 possible colors.

Hardcopy: Hardcopy refers to printed output. A printer prints characters or images on paper or another medium. Resolution of the image is measured by dpi (dots per inch), with more dots producing greater sharpness. Two types of printers are impact printers and nonimpact printers. Impact printers form images by striking a print hammer or wheel against an inked ribbon, leaving an image on paper; one type is the dot-matrix printer, which contains a print head of small pins. Nonimpact printer form characters or images without direct physical contact between printing mechanism and paper. Three types of nonimpact printers are laser, ink-jet, and thermal. A laser printer creates images with dots like a photocopying machine; the printer uses a page description language, software that describes the images to the printer. An ink-jet printer sprays electrically charged droplets of ink at high speed onto paper. A thermal printer uses colored waxes and heat to burn dots onto special paper. Another category of printer is the multifunction printer, which combines printing, scanning, copying, and faxing in one device.

Other Output: Other forms of output are sound, voice, and video. Sound-output devices produce digitized sound. Voice-output devices convert digital data into speech-like sounds. Video consists of photographic images, played at 15–29 frames per second; in one form of video output called videoconferencing people have online meetings using computers and communications devices that enable them to see and hear one another.