III. Read the text and do the tasks following it

The two basic categories of computer-produced output are (1) output to be used immediately by people and (2) output in a computer-usable form to be stored and then used later by the computer and people. Output can be in hardcopy form, which is generally thought of as being tangible, and softcopy form, which is thought of as intangible.

The second most commonly used output form is a softcopy one — the video display image. The two types of display screen used most often are a computer terminal connected to a large computer system and a monitor attached to a microcomputer system. When computer display devices are not readily available and information has some value over time, it is most often produced in hardcopy form. When computer display devices are readily available and information must be accessed quickly, it is often produced in softcopy form.

The main hardcopy output devices are printers and plotters. A printer can print characters, symbols, and sometimes graphics on paper. Printers are categorized according to whether or not the image produced is formed by physical contact of the print mechanism with the paper. Impact printers make contact; nonimpact printers do not.

Impact printers usually form images by pressing an inked ribbon against the paper with a hammerlike mechanism. A letter-quality printer, like a typewriter, presses fully formed characters against the ribbon. A dot-matrix printer uses separate pinlike hammers to form characters out of dot patterns.

Dot-matrix printers, because they do not print fully formed characters, are more flexible and can be used to print graphics in black or in colors.

Large computer systems often use special high-speed printers, called line printers, because they print a whole line at a time. Three common types of line printers are drum printers, band or belt printers, and chain printers.

The main categories of nonimpact printers are ink-jet printers, thermal printers, and laser printers. These printers make much less noise than impact printers. Ink jet printers, which are about as fast as dot-matrix printers, form images with tiny droplets of ink fired through a plate with holes drilled in it. Color ink-jet printers are used to produce graphics; however, ink jets can get clogged, and the image quality is not considered to be as good as that produced by plotters.

Thermal printers use heat to produce an image on specially treated paper. They are very quiet; however, they are slow and the special paper is expensive.

Laser printers are nonmechanical, nonimpact printers. Because the process has no print heads that move or print hammers that fire, the result is high speed and quiet operation. Laser printers work somewhat like photocopying machines. They use laser beams to transfer images to sensitive paper that is then coated with toner — the toner sticks to the spots sensitized by the laser.

Laser printers print a page at a time and can produce very high quality images, so they are often used for graphics. Since their prices have fallen, small laser printers are now within reach of users wanting a high-quality desktop printer.

They are frequently used in desktop publishing, which uses microcomputers, special software packages, and laser printers to produce material ready to be published. However, the small, affordable desktop laser printers do not yet produce color.

A plotter is most often used for producing graphics because it can output free-form drawings on paper in color.

The main softcopy output devices are cathode-ray tube (CRT) video screens and flat video screens.

CRTs can display images in one color (monochrome) or several colors. The RGB (red, green, blue) monitor uses three electron guns to illuminate red, green, and blue phosphors.

The most notable disadvantages of CRTs are their large size (to accommodate the electron gun setup), their high rate of power consumption, and their fragility.

The disadvantages of the CRT and rising interest in portable and laptop computers led to the development of flat screen technology, which is becoming a favored alternative to the CRT. The three most common types of flat panel displays are liquid crystal display (LCD), electroluminescent (EL) display, and gas plasma display.

Voice output systems can be used in situations where hardcopy is inappropriate and commonly used softcopy output devices are inconvenient.

As with input and storage, care must be taken to ensure that output is responsibly generated, shared, and disposed of. Control methods should be established to ensure that only authorized users see sensitive output and that output is properly secured.