Input devices and output devices are computer hardware that enable an operator to interact with the computer. Without input devices, a computer user would not be able to feed instructions to, or send and store information in, a computer; without output devices, the computer would not be able to give processed information back to the user.
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In computing, data input comes before data output. When you play an audio clip stored in disk, all the processes you carry out, including double-clicking the file, are inputs. You instruct the computer by using input devices to open a folder, locate the file, load the media player and play the audio clip. The computer takes in these instructions, executes them and gives you an output in the form of sound from the speakers. The same sequence is carried out in all computing processes, whether you edit a word document or browse the Internet.
Common Input Devices
Common input devices include mouse, keyboard, scanner, microphone and web-cam. The mouse and the keyboard are the most important input devices as all programs, including the operating system (OS), are designed to be navigated through and controlled with these devices. The mouse, a pointing device, is a small hemispherical object with a flat bottom; the contours fit into the palm of the hand, translating physical motions of the operator to cursor movement on the screen. In laptop computers, the mouse has been replaced with a flat, pressure-sensitive panel, operated by a finger. Another critical input device, the keyboard is a flat panel with rows of alphanumeric keys and other special keys with unique computing functions.
Common Output Devices
The most common output devices in modern computers are the display monitor, speaker, printer and the sound and video cards. The monitor works in conjunction with the video card, sometimes referred to as the graphics adapter, to generate and display images.The display monitor in a modern computer is flat-panel LCD screen able to display bright images with full clarity. Size of the display unit may vary, depending on computer function and setting—usually it is between 14 and 21 inches. Computer speakers play sounds, based on signals from the audio card. In a modern computer, the speakers can either be integrated into the hardware or added as a peripheral device.
Accessibility is a point of difference between input and output devices. An input device is used to take instructions from a user and give it to the computer and therefore has to be easily accessible to the user. If the mouse, instead of being on top of the table, was inside the computer's tower casing, it would be cumbersome (and dangerous) to operate the device. Output devices, on the other hand, do not rely on any form of physical contact with the computer user and may be present as an internal component. Examples are the expansion cards (sound and video) that are fitted into slots in the motherboard.
Physical Attributes and Price
Input devices are usually smaller in size than output devices and have physical attributes that emphasize on comfort and ease-of-use. Input devices typically handle data input through buttons, lens or microphone. Output devices are larger, and emphasize on quality and size of output. Most input devices, being smaller and easier to manufacture, cost less than output devices—keyboards and mice are more affordable than printers and LCD monitors.