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| Table 9.1 Some data rates for traditional data presentation devices. | | Data Rate | | Sensors | 1 Bps1 KBps | | Keyboard entry | 10 Bps | | Communications line | 30 Bps200 KBps | | CRT display | 2 KBps | | Line printer | 15 KBps | | Tape cartridge | 0.52 MBps |
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| Table 9.2 Some parameters for traditional I/O storage devices. | | Access Time | Data Rate | Capacity (bytes) | | Disk | 20 ms | 4.5 MBps | 1 GB | | Tape | O (sec)a | 36 MBps | 0.62.4 GB (per cartridge) | | aOrder of seconds |
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| Table 9.3 Some parameters for newer multimedia I/O transport devices. |
| | Data Rates | Maximum Delay | | Graphics | 1 MBps | 15 sec | | Video | 100 MBps | » 20 ms | | Voice | 64 Kbps (8KBps) | 50300 ms |
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Audio is one of the most demanding of the data presentation media, since it is highly user-intolerant of lapses or clips in the message presentation process. Each of these mediagraphics, video, voicerepresents an extraordinary challenge in processor design itself. The data they process can only be done by an ensemble of high-speed processors with associated transducers, filters, etc. (such as found in scanners and other electronic media devices). In this chapter, we treat only the role of I/O as storage in the processing system. Treatment of the various presentation media would require a separate treatise for each. |
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9.2 Evolution of I/O Systems Organization |
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The systems organization and functionality of I/O devices and their controllers have changed significantly over time. These changes have decoupled the processing of user programs from the processing of I/O requests. In the earliest I/O configurations, the processor and memory were intimately involved with the management of an I/O request [269]. |
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In these systems, the processor-memory bus forms the basic interface to the I/O device controller. This memory bus is usually asynchronous and |
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