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

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Chapter 11 I/O Management  and Disk Scheduling Seventh Edition By William Stallings Operating  Systems: Internals  and  Design  Principles
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Operating Systems: Operating Systems: Internals and Design Principles Internals and Design Principles n 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,  erbert Simon
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    External devices that engage in I/O with computer  systems can be grouped into three categories:
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Devices differ in a number of areas:
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Three techniques for performing I/O are: Programmed I/O 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 Interrupt-driven I/O the processor issues an I/O command on behalf of a process if non-blocking – processor continues to execute instructions from the process  that issued the I/O command 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 Direct Memory Access (DMA) a DMA module controls the exchange of data between main memory and an I/O  module
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Techniques for Performing I/O
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Efficiency Major effort in I/O design Important because I/O operations  often form a bottleneck Most I/O devices are extremely  slow compared with main  memory and the processor The area that has received the  most attention is disk I/O Generality Desirable to handle all devices in a  uniform manner Applies to the way processes view  I/O devices and the way the  operating system manages I/O  devices and operations Diversity of devices makes it  difficult to achieve true generality Use a hierarchical, modular  approach to the design of the I/O  function
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Functions of the operating system should be separated according to their  complexity, their characteristic time scale, and their level of abstraction Leads to an organization of the operating system into a series of layers Each layer performs a related subset of the functions required of the  operating system Layers should be defined so that changes in one layer do not require  changes in other layers
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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 No Buffer Without a buffer, the OS  directly accesses the device  when it needs
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