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Chapter 9
I/O and the Storage Hierarchy |
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The processor and memory are dependent on the rest of the system, especially on input-output devices that provide the basic transport mechanism for bringing new data and programs into the processor and providing results to the user. On first inspection, the configuration and variety of special-purpose I/O devices that can be coupled to a system give the impression of a very confusing and complex process of systems design. Yet, the system performance depends on the relationship between the processor-memory and these I/O devices. |
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I/O is important! The access time and transport rate of I/O devices frequently limit overall system performance. The execution of various input/output functions is quite time-consuming and usually involves a great deal of processor capability in managing various I/O processes. |
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There are three distinct types of peripheral devices: |
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1. Devices that are used primarily to transport data between the processor and the user. These are also known data presentation devices. |
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2. Devices that are used to communicate data from one processor to another. These include various types of network interface facilities and are referred to as networking devices. |
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3. Devices that are used to store information as part of the processor storage hierarchy. These are the basic storage devices of the system. |
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Some I/O devices fulfill multiple functions. Tape cartridges and portable disk packs are examples of devices that play a dual role. The network interface is simply the communications medium that enables the processor to reach remote peripheral devices, whether they be used for further communications or for storage. |
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Data transport and data presentation devices present a significantly lower workload to the processor than the storage devices. Tables 9.1 and 9.2 |
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