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Devices for the Hand

With a pen-based system, you use a "pen" (also called a stylus) to write on a special pad or directly on the screen. Pen-based computers are handy for writing notes or selecting options from menus, but they are not well suited for inputting long text documents because handwriting-recognition technology has not yet achieved 100 percent reliability.

Touch-screen systems accept input directly through the monitor. Touch-screen systems are useful for selecting options from menus, but they are not useful for inputting text or other types of data in large quantities.

A game controller is a special input device that accepts the user's input for playing a game. The two primary types of game controllers are joysticks and game pads.

Optical Input Devices

Bar code readers, such as those used in grocery stores, can read bar codes, translate them into numbers, and input the numbers into a computer system.

Image scanners convert printed images into digitized formats that can be stored and manipulated in computers. An image scanner equipped with OCR software can translate a page of text into a string of character codes in the computer's memory.

Audiovisual Input Devices

Microphones can accept auditory input. Using speech-recognition software, you can use your microphone as an input device for dictating text, navigating programs, and choosing commands. To use a microphone or other audio devices for input, your computer must have a sound card installed. A sound card takes analog sound signals and digitizes them. A sound card can also convert digital sound signals to analog form.

PC video cameras and digital cameras can digitize full-motion and still images, which can be stored and edited on the PC or transmitted over a LAN or the Internet.

 

Monitors and Sound Systems

Monitors

Computer monitors are roughly divided into two categories: CRT and flat-panel displays.

Monitors can also be categorized by the number of colors they display. Monitors are usually monochrome, grayscale, or color. A CRT monitor works with one or more electron guns that systematically aim a beam of electrons at every pixel on the screen. Most LCD displays are either active matrix or passive matrix. When purchasing a monitor, you should consider its size, resolution, refresh rate, and dot pitch.

The video controller is an interface between the monitor and the CPU. The video controller determines many aspects of a monitor's performance; for example, the video controller lets you select a resolution or set the number of colors to display. The video controller contains its own on-board processor and memory, called video RAM.

PC Projectors

A PC projector is a portable light projector that connects to a PC. This type of projector is rapidly replacing traditional slide projectors and overhead projectors as a means for displaying presentations. Many PC projectors provide the same resolutions and color levels as high-quality monitors, but they project the image on a large screen. The newest PC projectors use digital light processing to project bright, crisp images. A DLP projector uses a special microchip that contains tiny mirrors to produce images.



Sound Systems

Multimedia PCs generally come with sound systems, which include a sound card, speakers, a CD-ROM or DVD drive, and a video controller.

 

Printers

Printers fall into two general categories: impact and nonimpact. Impact printers create an image on paper by using a device to strike an inked ribbon, pressing ink from the ribbon onto the paper. Nonimpact printers use various methods to place ink (or another colored substance) on the page.

When evaluating printers for purchase, you should consider four criteria: image quality, speed, initial cost, and cost of operation.

A dot matrix printer is a common type of impact printer. A dot matrix printer uses a print head, which contains a cluster of pins. The printer can push the pins out to form patterns, in rapid sequence. The pins are used to press an inked ribbon against paper, thus creating an image. The lowest resolution dot matrix printers have an array of nine pins; the highest resolution dot matrix printers have twenty-four pins. The speed of dot matrix printers is measured in characters per second.

An ink jet printer is an example of a nonimpact printer. It creates an image by spraying tiny droplets of ink onto the paper. Ink jet printers are inexpensive for both color and black printing, have low operating costs, and offer quality and speed comparable to low-end laser printers.

Laser printers produce higher-quality print and are fast and convenient to use, but they are also more expensive than ink jet printers. Laser printers are nonimpact printers. They use heat and pressure to bond tiny particles of toner (a dry ink) to paper. Laser printers are available in both color and black and white, and the highest end laser printers provide resolutions of 1200 dpi and greater.

Snapshot printers are specialized, small-format printers used to print small color photographs. Snapshot printers are popular among users who own digital cameras. Snapshot printers are fairly slow, and they can be more expensive to operate than standard ink jet or laser printers.

Thermal-wax, dye-sublimation, fiery, and IRIS printers are used primarily by print shops and publishers to create high-quality color images.

Plotters create large-format images, usually for architectural or engineering purposes, using mechanical drawing arms, ink jet technology, or thermal printing technology.


Date: 2015-12-11; view: 396


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