os1_3 - Modified from Lecture Slides for Operating System...

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Operating Systems : Overview of Operating Systems (Chapter 1 ~ Chapter 3) Sung-Yong Park, Ph.D. Department of Computer Science Sogang University Modified from Lecture Slides for Operating System Concepts (6 th Edition) by Silberschatz et. al. Page 2 What is an Operating System? ± A program that acts as an intermediary between a user of a computer and the computer hardware. ± Operating system goals: ± Execute user programs and make solving user problems easier . ± Make the computer system convenient to use. ± Use the computer hardware in an efficient manner.
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Page 3 Operating System Definitions ± Resource allocator – manages and allocates resources. ± Control program – controls the execution of user programs and operations of I/O devices . ± Kernel – the one program running at all times (all else being application programs). Page 4 Abstract View of System Components
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Page 5 Mainframe Systems ± Reduce setup time by batching similar jobs ± Automatic job sequencing – automatically transfers control from one job to another. First rudimentary operating system. ± Resident monitor ± initial control in monitor ± control transfers to job ± when job completes control transfers pack to monitor Page 6 Layout for a Simple Batch System
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Page 7 Multi-programmed Batch Systems Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. Page 8 OS Features for Multiprogramming ± I/O routine supplied by the system. ± Memory management – the system must allocate the memory to several jobs. ± CPU scheduling – the system must choose among several jobs ready to run. ± Allocation of devices.
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Page 9 Time Sharing Systems ± The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory). ± A job swapped in and out of memory to the disk. ± On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard. ± On-line system must be available for users to access data and code. Page
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os1_3 - Modified from Lecture Slides for Operating System...

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