Input & Output.Input Hardware consists of devices that translate data into a form the computer can process. The people-readable form of the data may be words, but the computer-readable form consists of binary 0s and 1s, or off and on electrical signals. Output Hardware consists of devices that translate information processed by the computer into a form that humans can understand. Such output may be in the form of words, numbers, sounds, and pictures.
Input Hardware.Input Hardware may be divided into three categories: keyboards, pointing devices, and source-data entry devices.
Keyboards:Keyboards are devices that convert characters into electrical signals readable by the processor. There are two categories of keyboards. 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 a screen and a keyboard and can input and output but not process data. (2) An intelligent terminal has a screen, a 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 PCs or personal digital assistants (PDAs).
Pointing Devices:Pointing devices control the cursor or pointer on a screen and allow the user to select options displayed on the screen. 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, maneuvers a ball with the help of the surface on which the mouse is slid. 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 pen-like stylus on a screen; light pens, light-sensitive pen-like devices; and digitizers, which convert drawings to digital data – one example is the digitizing tablet.
Scanning & Reading Devices: Source-data entry devices create machine-readable data on magnetic media or paper, or feed it directly into the computer's processor. These include various scanning devices like bar-code readers, mark- and character-recognition devices, and fax machines; audio and video input devices (digital cameras); 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 of the most famous types of scanners is the flatbed scanner that works like a photocopier. Scanning technology has ushered in the new industry of electronic imaging. Another scanning device is the bar code reader, which reads the zebra-striped barcodes 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) 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) Speech-recognition systems process 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.
Output Hardware.Output hardware converts machine-readable information into people-readable form. Three common types of outputs are softcopy, hardcopy, and other.
Softcopy:Softcopy refers to printed data that is not printed, 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; color depth, which is the amount of information expressed in bits, that is stored in a dot; and by refresh rate, the number of times per second pixels are recharged. Two common 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 crystals create images by transmitting or blocking light. Flat-panel screens are either active-matrix display, in which a unique transistor controls each pixel on the screen, or passive-matrix display, in which a transistor controls a row or a column of pixels. The common color and resolution standards for monitors are SVGA (the most common), which can produce 16 million possible colors, XGA, which can produce 65,536 possible colors, SXGA which is used by graphic designers and programmers, UXGA which can support up to 16.8 million colors, and QXGA which is used for large LCD screens for computer users needing to view extreme details.
Hardcopy:Hardcopy refers to a printed output. A printer prints characters or images on paper or some other medium. Resolution of the image is measured by dpi (dots per inch), with more dots producing greater sharpness. The 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 printers, which contains a print head of small pins. Nonimpact Printers form characters or images without direct physical contact between printing mechanism and paper. The three types of nonimpact printers commonly used 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 printers 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. A special kind of printer, the plotter, which may be ink-jet or electrostatic, produces high-quality graphics, such as maps, that are too large for regular printers. 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.
The Future of Input & Output. Increasingly, input will be performed in remote locations and will rely on source data automation. Future source data automation will include high-capacity bar codes, 3-D scanners, more sophisticated touch devices, smarter smart cards, more diverse sensors, better voice recognition, smaller electronic cameras, more sophisticated biometric devices, and even brainwave input devices.
Output, too, is being performed in remote locations. On the horizon are better, cheaper, and larger display screens; higher-fidelity audio using wavetable synthesis and three-dimensional sound; and "real-time" video using digital wavelet theory. Thanks to 3-D technology, three-dimensional images can appear on computer displays and, through VRML software, users of the World Wide Web can experience 3-D "virtual worlds."