Chapter11-OS7e - Operating Systems: Internals and Design...

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Chapter 11 I/O Management  and Disk Scheduling n Seventh Edition By William Stallings Operating  Systems: Internals  and  Design  Principles
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Operating Systems: Internals and Design Principles An artifact can be thought of as a meeting point—an  “interface” in today’s terms between an “inner”  environment, the substance and organization of the  artifact itself, and an “outer” environment, the  surroundings in which it operates. If the inner  environment is appropriate to the outer environment, or  vice versa, the artifact will serve its intended purpose. —  THE SCIENCES OF THE ARTIFICIAL,  Herbert Simon
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Categories of I/O Devices     External devices that engage in I/O with computer  systems can be grouped into three categories:
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Differences in I/O Devices n Devices differ in a number of areas:
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Data Rates
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Organization of the I/O  Function n Three techniques for performing I/O are: n Programmed I/O n the processor issues an I/O command on behalf of a process to an I/O module;  that process then busy waits for the operation to be completed before  proceeding n Interrupt-driven I/O n the processor issues an I/O command on behalf of a process n if non-blocking – processor continues to execute instructions from the  process that issued the I/O command n if blocking – the next instruction the processor executes is from the OS,  which will put the current process in a blocked state and schedule another  process n
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Techniques for Performing I/O
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Evolution of the I/O  Function
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Direct  Memory  Access
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Alternative DMA Configurations
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Design Objectives n Efficiency n Major effort in I/O design n Important because I/O  operations often form a  bottleneck n Most I/O devices are extremely  slow compared with main  memory and the processor n The area that has received the  most attention is disk I/O n Generality n Desirable to handle all devices  in a uniform manner n Applies to the way processes  view I/O devices and the way  the operating system manages  I/O devices and operations n Diversity of devices makes it  difficult to achieve true  generality n Use a hierarchical, modular  approach to the design of the 
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Hierarchical Design n Functions of the operating system should be separated according to their  complexity, their characteristic time scale, and their level of abstraction n Leads to an organization of the operating system into a series of layers n Each layer performs a related subset of the functions required of the  operating system n Layers should be defined so that changes in one layer do not require  changes in other layers
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A Model of I/O  Organization
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Buffering n Perform input transfers in advance of requests being made and perform  output transfers some time after the request is made
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No Buffer n Without a buffer, the OS  directly accesses the device  when it needs
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Single Buffer n Operating system assigns a  buffer in main memory for an  I/O request
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This note was uploaded on 12/14/2011 for the course CS 490 taught by Professor Weisskop during the Fall '11 term at University of Alabama - Huntsville.

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Chapter11-OS7e - Operating Systems: Internals and Design...

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