Computer Output Devices

Computer Output Devices

An output device is any hardware device that makes information from a computer available to the user. A computer produces output using the combination of output devices, media, and software available with a particular system. Some output devices include monitors and printers.

Monitors

A monitor is a fundamental component of a computer system and is the most common soft copy output mechanism for displaying text, images, graphics, and video on a screen. Available in a variety of shapes, sizes, costs, and capabilities, monitors allow users to view information temporarily.

CRT Monitor

An early type of monitor for desktop computers was the cathode ray tube (CRT) monitor (see Figure 1). A CRT is a large, sealed glass tube housed in a plastic case. The front of the tube is the screen. A cable at the rear of the monitor plugs into a graphics adapter board on the motherboard inside the system unit. An electric cord on the monitor plugs into an electrical outlet. CRT monitors use the same cathode ray tube technology used in television sets, so most are fairly large and bulky.

Flat-Panel Monitor

A flat-panel monitor uses a technology that allows it to be smaller, thinner, and lighter than CRT monitors (see Figure 2). An additional benefit of these lightweight compact screens is that they consume less power compared to CRT monitors. The majority of flat-panel displays use liquid crystals to produce information on the screen. In a liquid crystal display (LCD), liquid crystals are sandwiched between two sheets of material. An electric current passing through the crystals causes them to twist. This twisting effect blocks some light waves and allows other light waves to pass through, creating image on the screen.

Printers

A printer is the most common type of device for producing hard-copy output on a physical medium, such as paper or transparency film. Almost all printers are capable of printing in either portrait or landscape format. In portrait format, a printed page is taller than it is wide. Portrait format is usually used for letters, memos, reports, and newsletters. In landscape format, a printed page is wider than it is tall. Landscape format is best suited for financial spreadsheets and other types of tabular reports. Two types of printers include ink-jet printers and laser printers.

Ink-Jet Printer

An ink-jet printer is a nonimpact printer that forms characters and images by spraying thousands of tiny droplets of electrically charged ink onto a sheet of paper as the sheet passes through the printer (see Figure 3). Most ink-jet printers use two or more ink cartridges, one for black print and one or more for color printing. Each cartridge has multiple holes, called nozzles. During printing, combinations of tiny ink droplets are propelled through the nozzles by heat and pressure onto the paper, forming characters and images.

Laser Printer

A laser printer is a nonimpact printer that produces output of exceptional quality using a technology similar to that of a photocopy machine. Laser printers are used for any printing application, including those requiring output of printing-press quality material (see Figure 4). Their speed and ability to produce clear, crisp text and images have made them the fastest growing segment of the printer market. A laser printer creates text and graphics on a rotating metal drum using a laser beam. During printing, components inside the printer read characters and relay them to a printer device called a laser mechanism. A laser beam produces characters and images on a rotating drum inside the printer by altering the electrical charge wherever the beam strikes the drum. The charges produce tiny magnetic fields (dots) on the drum, forming characters. As the drum rotates, it picks up an ink-like powder called toner, similar to copy machine toner. The sensitive dots on the drum are then deposited onto the paper. Using heat and pressure, a set of rollers fuses the toner onto the paper, forming the printed image.