Output devices are machines that can represent—or output—data that a computer generates. The devices do this using either auditory or visual mechanisms. According to psychology professor Kent L. Norman of the University of Maryland (See Reference 1), the three most common output devices for a computer are monitors, audio outputs and printers.
Also known as visual display units, computer monitors allow computers to create temporary visual representations of data. Monitors traditionally produced these visualizations using cathode ray tube, or CRT, technology. This technology uses a vacuum tube to shoot electrons at a screen, which generates colored dots or pixels of phosphorescence. New computer monitor technologies include liquid crystal display or LCD, which creates pixels by applying electrical current to a layer of liquid crystal molecules, and plasma, which creates pixels by applying electrical current to a mixture of noble gases. While most traditional computer monitors have an aspect ratio of 4:3, more modern monitors have an aspect ratio of 16:9, which enables them to support the wide-screen video format.
Audio output devices allow computers to produce auditory representations of data such as WAV, MP3 and MIDI files. The most common audio outputs for computers are speakers, which send sound waves outward by vibrating specialized cones. Speakers create these vibrations via electrical stimulation. Other popular audio outputs for computers are headphones, which create vibrations just like speakers. However, instead of projecting sound outward, headphones focus sound inward toward a listener.
Printers are output devices that enable computers to create permanent visual representations of data such as JPG, GIF and PNG files. Traditional printers rely on dot-matrix technology, which uses wires to stamp tiny ink dots onto paper. More modern computer printers typically rely on either inkjet or laser technology. While inkjet printers create images my spraying droplets of ink onto paper, laser printers create images by shooting dense monochromatic beams of light at photosensitive drums, which then transfer toner, or dry ink, onto paper.
Hard Copy vs. Soft Copy
You can classify the most common output devices for computers as either hard copy or soft copy. While hard copy devices, such as printers, produce physical, tangible representations of data, soft copy devices, such as monitors, produce intangible representations of data: the images that appear on screen do not exist outside the computer. Audio outputs are also soft copy outputs, as the sounds they generate do not become permanently externalized. Creating a hard copy of audio would require the use of a CD burner or other less common output device.