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and present data that have been processed (output). A keyboard is a common input device. Another is a mouse, a pointing device. A video display is a common output device, as are printers and liquid crystal display (LCD) screens. |
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Input/Output (I/O) Devices The parts of the computer that accept data to be processed (input) and present the results of that processing (output). |
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For the most part, computers simply move and combine data in memory. The differences among various computers basically involve the size of their memories and the speed with which data can be recalled, the efficiency with which data can be moved or combined, and limitations on I/O devices. |
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When a program is executing, the computer proceeds through a series of steps, the fetch-execute cycle: |
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1. The control unit retrieves (fetches) the next coded instruction from memory. |
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2. The instruction is translated into control signals. |
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3. The control signals tell the appropriate unit (arithmetic/logic unit, memory, I/O device) to perform (execute) the instruction. |
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4. The sequence repeats from step 1. |
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Computers can have a wide variety of peripheral devices (see Figure 1-10). An auxiliary storage device, or secondary storage device, holds coded data for the computer until we actually want to use the data. Instead of inputting data every time, we can input it once and have the computer store it onto an auxiliary storage device. Whenever we need to use the data, we tell the computer to transfer the data from the auxiliary storage device to its memory. An auxiliary storage device therefore serves as both an input and an output device. Typical auxiliary storage devices are magnetic tape |
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