08_Operating System Support

08_Operating System Support - William Stallings Computer...

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William Stallings Computer Organization and Architecture 7 th Edition Chapter 8 Operating System Support
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Objectives and Functions Convenience Making the computer easier to use Efficiency Allowing better use of computer resources
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Layers and Views of a Computer System
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Operating System Services Program creation Program execution Access to I/O devices Controlled access to files System access Error detection and response Accounting
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O/S as a Resource Manager
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Types of Operating System Interactive Batch Single program (Uni-programming) Multi-programming (Multi-tasking)
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Early Systems Late 1940s to mid 1950s No Operating System Programs interact directly with hardware Two main problems: Scheduling Setup time
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Simple Batch Systems Resident Monitor program Users submit jobs to operator Operator batches jobs Monitor controls sequence of events to process  batch When one job is finished, control returns to  Monitor which reads next job Monitor handles scheduling
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Memory Layout for Resident Monitor
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Job Control Language Instructions to Monitor Usually denoted by $ e.g. $JOB $FTN ... Some Fortran instructions $LOAD $RUN ... Some data $END
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Desirable Hardware Features Memory protection To protect the Monitor Timer To prevent a job monopolizing the system Privileged instructions Only executed by Monitor e.g. I/O Interrupts Allows for relinquishing and regaining control
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Multi-programmed Batch Systems I/O devices very slow When one program is waiting for I/O, another  can use the CPU
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Single Program
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Multi-Programming with Two Programs
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Multi-Programming with Three Programs
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Utilization
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Time Sharing Systems Allow users to interact directly with the computer i.e. Interactive Multi-programming allows a number of users to  interact with the computer
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Scheduling Key to multi-programming Long term Medium term Short term I/O
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Long Term Scheduling Determines which programs are submitted for  processing i.e. controls the degree of multi-programming Once submitted, a job becomes a process for  the short term scheduler (or it becomes a swapped out job for the  medium term scheduler)
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Medium Term Scheduling Part of the swapping function (later…) Usually based on the need to manage multi- programming If no virtual memory, memory management is  also an issue
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08_Operating System Support - William Stallings Computer...

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