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I/O is a generic term applied to rather distinct data movement functions that are required from the computing system. The processor has a defined storage space. The I/O system does not have such an a priori limit on the number of stored or transferred messages. The data transfer role of I/O can be further broken down into three separate functions: |
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1. Data presentation and acquisition. |
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2. Network data communications. |
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Data presentation/acquisition provides the ultimate use of, and input to, processor information, while the network is responsible for moving data among processors. |
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Storage devices provide the higher levels of the storage hierarchy. I/O represents the archive of the data storage space that the processor may access. Most processor performance issues are related to the storage role of I/O, as most of the I/O requests come from the processor to manage storage requests. |
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illustrate some data transfer requirements for a spectrum of devices. Data transport devices either bring new information into, or remove information from, the memory hierarchy. They may directly affect the size and structure of the storage address space as seen by the processor. |
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While traditional data entry/data presentation devices have been rather slow compared to demands of the storage system, the situation is changing (Table 9.3). Computers are increasingly being used to manage multimedia documents consisting of: |
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Video ("moving pictures"). |
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Voice (both recognition and answerback). |
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Each medium requires enormous dedicated computation. Special-purpose processors have been designed to manage sophisticated graphics representations (color rendering, 3-D modeling, animation, etc.). The management of the graphic image can require up to 510 high-speed microprocessors. |
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The problem of video is simply the acceleration of the graphics problem, since a new image can be created once every 1/30th of a second (33 milliseconds). Of course, data compression and interpolation techniques can be used to significantly reduce the obvious extraordinary network load required for real-time video processing. |
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Voice is another very demanding data presentation format. The equivalent of 1664 Kbps of digitized voice signals requires an extraordinary amount of processing to either create or recognize various phonemes in real time. |
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