Lecture 07 - - Understanding Operating Systems Sixth...

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Understanding Operating Systems Sixth Edition Chapter 7 Device Management
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Understanding Operating Systems, Sixth Edition 2 Learning Objectives After completing this chapter, you should be able to describe: Features of dedicated, shared, and virtual devices Differences between sequential and direct access media Concepts of blocking and buffering and how they improve I/O performance Roles of seek time, search time, and transfer time in calculating access time
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Understanding Operating Systems, Sixth Edition 3 Learning Objectives (cont'd.) Differences in access times in several types of devices Critical components of the input/output subsystem, and how they interact Strengths and weaknesses of common seek strategies, including FCFS, SSTF, SCAN/LOOK, C-SCAN/C-LOOK, and how they compare Different levels of RAID and what sets each apart from the others
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Understanding Operating Systems, Sixth Edition 4 Types of Devices Despite the multitude of devices that appear (and disappear) in the marketplace and the swift rate of change in device technology, the Device Manager must manage every peripheral device of the system. It must maintain a delicate balance of supply and demand – balancing the system’s finite supply of devices with users’ almost infinite demand for them.
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Understanding Operating Systems, Sixth Edition 5 Types of Devices (cont’d) Device management involves four basic functions: Monitoring the status of each device, such as storage drives, printers, and other peripheral devices; Enforcing preset policies to determine which process will get a device and for how long; Allocating the devices; Deallocating them at two levels: At the process (or task) level when an I/O command has been executed and the device is temporarily released; At the job level when the job is finished and the device is permanently released.
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Understanding Operating Systems, Sixth Edition 6 Types of Devices (cont’d) The system’s peripheral devices generally fall into one of three categories: Dedicated Shared Virtual The differences are a function of the characteristics of the devices, as well as how they’re managed by the Device Manager.
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Understanding Operating Systems, Sixth Edition 7 Types of Devices (cont’d) Dedicated Devices Are assigned to only one job at a time. They serve that job for the entire time the job is active or until it releases them. Some devices demand this kind of allocation scheme, because it would be awkward to let several users share them. Example: tape drives, printers, and plotters Disadvantages They must be allocated toa single user for the duration of a job’s execution, even though the device is not used 100% of the time.
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Understanding Operating Systems, Sixth Edition 8 Types of Devices (cont'd.) Shared Devices Can be assigned to several processes. For example – a disk (DASD) can be shared by
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This note was uploaded on 10/15/2011 for the course COMP 1210 taught by Professor M.izzo during the Spring '11 term at Community college of RI.

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Lecture 07 - - Understanding Operating Systems Sixth...

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