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| The other parts of the computer system, outside the system unit, are primarily used as a means of communicating with the CPU to send in instructions and data and get out information. Devices used to communicate with the CPU are known as input and output (or I/O) devices. Input devices are those that allow you to pose questions and issue commands. Output devices are what allow the computer to talk back, providing you with answers or asking you for additional information. |
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| In personal computers, the most common input device is the keyboard. Using a keyboard, you can type text and issue commands. |
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| The second most common input device is a mouse. The mouse is a hand-held pointing device that allows you to point to words or objects on the computer screen. Pressing the buttons on the mouse (called pressing or clicking, depending on how fast you do it) lets you make selections on your screen. |
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| You can also communicate with your computer using an input device called a trackball, which is a pointing device that resembles a ball nestled in a square cradle and serves as an alternative to a mouse. |
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| Another input device is a scanner, which allows you to copy an image (such as a photograph, a drawing, or a page of text) into your computer, translating it into a form that the computer can store and manipulate. |
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| A joystick is an input device that lets you manipulate the various people, creatures, and machines that populate computer games. |
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| A digital camera lets you capture a photographic image in digital (that is, computer-readable) form and then lets you transfer that image directly from camera to computer. |
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| The most common output device is the display screen, which the computer uses to display instructions and present information. Computer screens go by many names, including monitor, VDT (video display terminal), and CRT (for cathode ray tube, the technology used in most desktop computer screens). |
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| A printer generates paper copies of your data. Like monitors, printers come in many shapes and sizes and generate output ranging from the old grainy-looking computer printouts to color printouts that rival the clarity of offset printing. |
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| These days, many computers also come equipped with a sound board-a device that resides inside the system unit and allows your computer to generate sounds and music. Most computers have some kind of speakers. |
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