Unit 4.
Topic: Input/Output devices.

II. Reading
1. Read the text and see if you correctly classified the devices.
   A. Input devices are pieces of hardware which allow us to enter information into the computer. The most common are the keyboard and the mouse. We can also name a lightpen, a scanner, a trackball, a graphics tablet, a joystick, etc.
   B. A mouse is a palm-sized device, slightly smaller than a pack of cards. On top of the mouse there are one or more buttons for communicating with the computer. A 'tail' or wire extends from the mouse to a connection on the back of the computer. The mouse is designed to slide around on your desktop. As it moves, it moves an image on the screen called a pointer or mouse cursor which mimics the movements of t he-mouse on your desktop. What makes the mouse especially useful is that it is a very quick way to move around on a screen. The mouse also issues instructions lo the computer very quickly. Mice are also widely used in graphics applications because they can do things that are difficult, if not impossible, to do with keyboard keys. The buttons on the mouse are used to select items at which the mouse points. You position the pointer on an object on the screen, for example, on a menu or a tool in a paint program, and then you press the mouse button to 'select' it. Mice are also used to load documents into a program.
   C. After the entered information has been processed internally, we can see the results on the visual display unit. To obtain the permanent copy of these results, we can use plotters, printers or video recorders. The monitor plays an important part here.
   D. The characters and pictures that we see on the screen are made up of dots, also called picture elements (pixels). The total number of pixels in which the display is divided both horizontally and vertically is known as the resolution. Typical resolutions are 640 x 480 or 1,024 x 768 pixels. The cathode ray tube of the monitor is very similar to that of a TV set. Inside the tube there is an electron beam which scans the screen and turns on or off the pixels that make up the image. The beam begins m the top left corner, and scans the screen from left to right in a continuous sequence; this sequence is repeated 50, 60 or 75 times per second, depending on the system. What we see on the screen is created and then stored in an area of RAM, so that there is a memory cell allocated to each pixel. This type of display is called bit-mapped. On colour displays, there are three electron guns at the back of the monitor's tube. Mach electron gun shoots out a beam of electrons; there is one beam for each of the three primary colours: red, green and blue. These electrons strike the inside of the screen.
   E. The monitor is controlled by a separate circuit board called the display adaptor. Some computers have flat liquid-crystal displays which use a grid of crystals and polarizing filters to show the image.
(adapted from Infotech, Remacha Esteras, p. 29, p. 35)
    Скачать>>>