ch04 - Chapter 4 Processor Management Understanding...

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Chapter 4 Processor Management Understanding Operating Systems, Fourth Edition
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Understanding Operating Systems, Fourth Edition 2 Objectives Objectives You will be able to describe: The difference between job scheduling and process scheduling, and how they relate The advantages and disadvantages of process scheduling algorithms that are preemptive versus those that are nonpreemptive The goals of process scheduling policies Up to six different process scheduling algorithms The role of internal interrupts and the tasks performed by the interrupt handler
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Understanding Operating Systems, Fourth Edition 3 Overview Overview Program (Job): A unit of work that has been submitted by user to an operating system An inactive unit, such as a file stored on a disk Process (Task): An active entity, which requires a set of resources, including a processor and special registers, to perform its function A single instance of an executable program
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Understanding Operating Systems, Fourth Edition 4 Overview (continued) Overview (continued) Processor (CPU): performs calculations and executes programs In single-user systems: Processor is busy only when user is executing a job, at all other times it is idle Processor management is simple In a multiprogramming environment: Processor must be allocated to each job in a fair and efficient manner Requires scheduling policy and a scheduling algorithm
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Understanding Operating Systems, Fourth Edition 5 Overview (continued) Overview (continued) Interrupt: A hardware signal that suspends execution of a program and activates the execution of interrupt handler Context Switch: Saving a job’s processing information in its PCB when interrupted Context switching occurs in all preemptive policies
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Understanding Operating Systems, Fourth Edition 6 Job Scheduling Versus Job Scheduling Versus Process Scheduling Process Scheduling Processor Manager has two submanagers: Job Scheduler: In charge of job scheduling Initiates the job based on certain criteria Process Scheduler: In charge of process scheduling Assigns the CPU to execute processes of those jobs placed on READY queue by Job Scheduler
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Understanding Operating Systems, Fourth Edition 7 Job Scheduling Versus Process Job Scheduling Versus Process Scheduling Scheduling (continued) (continued) Job Scheduler (High level scheduler): Initiates the job based on certain criteria Puts jobs in a sequence that uses all system’s resources as fully as possible Strives for balanced mix of jobs with large I/O interaction and jobs with lots of computation Tries to keep most system components busy most of time
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Understanding Operating Systems, Fourth Edition 8 Job Scheduling Versus Process Job Scheduling Versus Process Scheduling Scheduling (continued) (continued) Process Scheduler (Low level scheduler): Determines which jobs will get the CPU, when, and for how long Decides when processing should be interrupted Determines which queues the job should be moved to during its execution Recognizes when a job has concluded and should be terminated
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ch04 - Chapter 4 Processor Management Understanding...

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