Peripheral devices :
Peripheral devices are devices that are attached to a computer system. Input devices, output devices, and the various storage units are all peripheral devices. These devices augment the basic services provided by the computer system. The input/output (I/O) devices act as a means of communication between the computer and the end user while the storage devices act as warehouses for the inputs and the outputs. Even when peripheral devices are connected to the computer, they are external to the processing unit. The computer will continue to work even when a peripheral device is disconnected.
Input devices:
Input devices are the devices that are used for entering data and instructions into the input unit of the computer system. Some of the main input devices are discussed here.
Keyboard
The keyboard of a computer resembles the keyboard of a typewriter. It consists of alphanumeric keys (letters and numbers), punctuation keys (comma, colon, semicolon, etc), and special keys (control keys, arrow keys, function keys, etc). These keys are placed in the ‘Q-W-E-R-T-Y' layout, similar to those in a typewriter. When a key is pressed, electronic signals are generated. A keyboard encoder detects these signals and sends them to the CPU. The most popular keyboard is the one with 101 keys.
Cordless or wireless keyboards are an advancement over the regular (wired or corded) keyboards. Cordless keyboards are similar to the regular keyboards. The only difference is that they are not connected to the computer system with cables, i.e., these computers do not have wires or cords. Cordless keyboards are sometimes combined with other cordless pointing devices such as cordless mice.
Mouse
The mouse is a handheld pointing device that controls the movement of the cursor or pointer on the monitor or the display screen. It is connected to the computer system through a cable. A mouse has one to four buttons (usually two or three) and can be used for clicking on an icon, selecting a text or an object, dragging the selected items, etc. An additional feature of a scroller has also been added in the later versions of the mouse. The scroller is used as a replacement of the keyboard scroll keys. It enables easy scroll up and scroll down facilities.
The optical mouse, laser mouse, wireless or cordless mouse, etc., are advancements over the regular mouse. An optical mouse has the ability to work on any surface. Compared to the regular mouse, an optical mouse does not have any moving parts. This results in less wear and tear, thus resulting in less chance of failure. Dust cannot get inside the optical mouse and interfere with the tracking sensors. It moves smoothly and works faster on any surface. Unlike the regular mouse, it does not require any special surface like a mouse pad. A laser mouse has a laser within it. Compared to the previously released types of mouse, the laser mouse facilitates a much smoother and much more accurate control of the cursor. Other features in a laser mouse include a scroller, a thin and flexible wire, and customized buttons.
Touchpad
In most of the laptop computers, the mouse is replaced by a touchpad. A touchpad is a very small, touch sensitive device that is placed in front of the keyboard.
The movement of a finger placed on the touchpad moves the cursor on the screen. In order to click, the user has to tap the pad or use the buttons in front of the pad which work like the mouse buttons.
Joystick
A joystick is a controlling device which is most often used for playing computer games or controlling robots in the manufacturing industry. It has a gearshift like lever which is used to move the pointer or cursor on the screen. Generally, joysticks are two dimensional with two sides of movement. Three-dimensional joysticks are also available. They are also used by flight simulators and other training simulators.
Trackball
A trackball is a pointing device that looks like a mouse that is lying on its back. Trackballs have a roller on top and selection buttons on the side. Though the way they function is similar to that of a mouse, trackballs are more stationary, do not occupy much space, and can be placed on any surface.
Light pen
Light pens are pointing devices that resemble pens and are connected to the visual display unit. These devices are used for selecting menu items or for drawing pictures. A light pen consists of a small tube that contains a photocell and an optical system. When the tip of the pen touches the screen, the photocell sends the corresponding signal to the CPU indicating the screen location.
Touch screens
A touch screen is used in place of a keyboard. Touch screens recognize the human touch. Using them, users can point to the selection on the screen using their fingers.
Digitizer
A digitizer is a device that uses the process of digitizing to create drawings and pictures. Digitizing is a process of converting analog signals into digital signals. It is used for converting graphic representations into digital data. A digitizer comprises a digitizer tablet which is connected to a pen-like stylus. This stylus is used to trace the image, store it in the RAM, and display it on the monitor.
Scanners
Scanners are devices that are designed to copy anything that is printed on a sheet of paper. They have the ability to analyze a picture or text and then convert it into a digital image. Scanners use Charge-Coupled Devices (CCDs) to digitize an image formed by a lens. Most scanners are equipped with Optical Character Recognition (OCR) software that automatically decodes imaged text into a text file. Using this technology, most of the printed or typed documents can be scanned and converted into text files.
Output Devices:
After entering the data and the instructions, processing takes place, and the final results of computation are generated. Users can obtain these results through the output devices. Given here are some of the commonly used output devices:
Monitors
The monitor is an on-screen display that acts as an interface between the user and the computer system. A computer monitor is also known as computer display as it enables the user to view the results of data processing. The image displayed on the monitor is generated by a video adapter. A video adapter is an expansion board that plugs into one of the computer expansion slots and connects the output of the computer system to the monitor. It converts the digital instructions given by the computer system to an analog signal that can be understood by the monitor. This signal in turn instructs the monitor to display the output. It determines the overall quality of the image that the monitor displays. The monitor has its own processing circuitry and memory called Video RAM (VRAM). The output on the screen is referred to as a soft copy, while the printed version is called the hard copy.
Printers
The most common form of obtaining computer output is by getting hard copies. These copies are obtained through an output device called a printer. Printers are devices that produce hard copies of information stored in computers on paper or on transparencies. Most of the printers are connected to the computer through a printer cable. Other types of printers called network printers have built-in network interfaces. These interfaces can be used by any user on the network. Printers are generally categorized by the way they create print characters. There are two basic types of print technologies namely, impact printers and non-impact printers.
Sound cards and speakers
Sound cards and speakers are the output devices that allow the users to receive an audio output from the computer system. The audio output generated by the computer system could be in the form of recorded sound files and even synthesized speech.
Plotters
Plotters are devices that are used for printing quality graphics and drawings on paper. These devices are different from printers as they use a pen for drawing lines, thus, producing continuous lines. Plotters can also draw different colors by using colored pens. These devices are very expensive compared to the printer and are widely used for engineering applications and by engineers, architects, surveyors, etc.
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