Computer Input and Output Devices

A personal computer would be useless if you could not interact with it because the machine could not receive instructions or deliver the results of its work. Input devices accept data and instructions from the user or from another computer system (such as a computer on the Internet).
Output devices return processed data to the user or to another computer system.
Computer input and output devices
Fig. 1: Computer input and output devices.

Computer Input Devices

The most common input device is the keyboard, which accepts letters, numbers, and commands from the user. Another important type of input device is the mouse, which lets you select options from on-screen menus. You use a mouse by moving it across a flat surface and pressing its buttons. Fig. 1 shows a personal computer with a keyboard, mouse, and microphone.
A variety of other input devices work with personal computers, too: (see Fig. 2)
» The trackball and touchpad are variations of the mouse and enable you to draw or point on the screen.
» The joystick is a swiveling lever mounted on a stationary base that is well suited for playing video games.
» A scanner can copy a printed page of text or a graphic into the computer's memory, freeing you from creating the data from scratch.
» A digital camera can record still images, which you can view and edit on the computer.
» A microphone enables you to input your voice or music as data.
Fig. 2: Varieties of input devices.

Computer Output Devices

The function of an output device is to present processed data to the user. The most common output devices are the monitor and the printer.
The computer sends output to the monitor (the display screen) when the user needs only to see the output. It sends output to the printer when the user requests a paper copy—also called a hard copy—of a document.
Just as computers can accept sound as input, (they can use stereo speakers or headphones as output devices to produce sound. Fig. 1 shows a PC with a monitor; printer; and speakers.
Some types of hardware can act as both input and output devices. A touch screen, for example, is a type of monitor that displays text or icons you can touch. When you touch the screen, special sensors detect the touch and the computer calculates the point on the screen where you placed your finger. Depending on the location of the touch, the computer determines what information to display or what action to take next.
Communications devices are the most common types of devices that can perform both input and output. These devices connect one computer to another—a process known as networking. The most common kinds of communications devices are modems, which enable computers to communicate through telephone lines or cable television systems, and network interface cards (NICs), which let users connect a group of computers to share data and devices.

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