Ch07_ECOA2e - Chapter 7 Input/Output and Storage Systems...

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Chapter 7 Input/Output and Storage Systems
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2 Chapter 7 Objectives Understand how I/O systems work, including I/O methods and architectures. Become familiar with storage media, and the differences in their respective formats. Understand how RAID improves disk performance and reliability, and which RAID systems are most useful today. Be familiar with emerging data storage technologies and the barriers that remain to be overcome.
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3 7.1 Introduction Data storage and retrieval is one of the primary functions of computer systems. One could easily make the argument that computers are more useful to us as data storage and retrieval devices than they are as computational machines. All computers have I/O devices connected to them, and to achieve good performance I/O should be kept to a minimum! In studying I/O, we seek to understand the different types of I/O devices as well as how they work.
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4 7.2 I/O and Performance Sluggish I/O throughput can have a ripple effect, dragging down overall system performance. This is especially true when virtual memory is involved. The fastest processor in the world is of little use if it spends most of its time waiting for data. If we really understand what’s happening in a computer system we can make the best possible use of its resources.
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5 7.3 Amdahl’s Law The overall performance of a system is a result of the interaction of all of its components. System performance is most effectively improved when the performance of the most heavily used components is improved. This idea is quantified by Amdahl’s Law: where  S  is the overall speedup;  f  is the fraction of work performed by a  faster component; and  k  is the speedup of the faster component.
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6 7.3 Amdahl’s Law Amdahl’s Law gives us a handy way to estimate the performance improvement we can expect when we upgrade a system component. On a large system, suppose we can upgrade a CPU to make it 50% faster for $10,000 or upgrade its disk drives for $7,000 to make them 250% faster. Processes spend 70% of their time running in the CPU and 30% of their time waiting for disk service. An upgrade of which component would offer the greater benefit for the lesser cost?
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7 7.3 Amdahl’s Law The processor option offers a 130% speedup: And the disk drive option gives a 122% speedup: Each 1% of improvement for the processor costs $333, and for the disk a 1% improvement costs $318. Should price/performance be your only concern?
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8 7.4 I/O Architectures We define input/output as a subsystem of components that moves coded data between external devices and a host system. I/O subsystems include:
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Ch07_ECOA2e - Chapter 7 Input/Output and Storage Systems...

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