Text A. PERIPHERALS
A peripheral is a device connected to a host computer, but not a part of it, and is more or less dependent on the host. It expands the host's capabilities, but does not form part of the core computer architecture. The examples are input/output devices such as printers, image scanners, drives, microphones, loudspeakers, webcams, and digital cameras.
A keyboard is a human interface device which is represented as a layout of buttons. Each button, or key, can be used to either input a linguistic
character to a computer, or to call upon a particular function of the computer. Traditional keyboards use spring-based buttons, though newer variations employ virtual keys. The way of connection is the same to printers.
A mouse is an input device that operates by controlling the position of the cursor (in the shape of an arrow) on the monitor. A mouse is a pointing device that combines the traditional cursor movements— accomplished by pressing arrow keys— with the means to select an object on the display screen. One or more buttons located on the top of the mouse enable you to choose options. Small portable computers sometimes use a built-in or attachable trackball in lieu of a mouse. Rolling the trackball with your fingertips produces the same results as moving the mouse.
Light pens, often used in stores, are able to input a large amount of data quickly by moving a light beam across a barcode. This converts the barcode into digital data that is usable by the computer. Other types of light pens are also used for computer-aided design (CAD) and pen-based computers; the latter interpret and convert human writing into computer form.
A scanner is an input device that acts like a miniature photocopy machine connected to a computer, copying graphic images into the computer and allowing typewritten pages to be entered without retyping. Scanners include both hand-held and desktop models. A scanner works by passing a beam of light across the original page or artwork and
sensing the reflected light; it then assembles this information into a data file that describes the images as rows of tiny dots, each one noted for its colour and brightness. That file is then passed on to the computer.
Several devices are used to get the output from the computer. Monitors, which look like television sets, quickly display and redisplay the computer's output. They are often called VDUs (video display units), VDTs (video display terminals), or simply screens. The image displayed on the screen is composed of many rows of tiny dots, called pixels (short for picture element). The number and size of pixels determine the resolution (sharpness and clarity) of the display.
The more pixels, the higher the resolution.
There are different types of display screens. The most common type is the LCD (liquid crystal display) monitor. It takes up little space and uses the same technology as that used for screens or notebooks. The CRT (cathode ray tube) is rather like a conventional TV. They can be monochrome or colour. Monochrome monitors show one colour, generally white, green, or amber, on a dark background. Colour monitors (often called graphics monitors) display text characters and graphic images in colour.
Speakers and headphones allow the user to hear audio data,
such as speech or music, through the computer.
Printers create paper copies, called hardcopies, of information sent from the computer. Printers for personal computers are connected to the computer by a cable through a port—the location through which the computer exchanges information with an external device. A port has a physical connector and an address, so that programs know where to send information. The two basic types of ports are serial and parallel.
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