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Lecture Operating systems: Lesson 6 - Dr. Syed Mansoor Sarwar

Lecture Operating systems: Lesson 6 - Dr. Syed Mansoor Sarwar. The main topics covered in this lesson include: process scheduling concepts; process creation and termination; process management in UNIX/Linux—system calls: fork, exec, wait, exit; sample codes; . | Operating Systems Lecture 6 Agenda for Today Review of previous lecture Process scheduling concepts Process creation and termination Process management in UNIX Linux system calls fork exec wait exit Sample codes Recap of the lecture 28 April 2022 Copyright Virtual University of Pakistan Review of Lecture 5 Browsing the UNIX Linux directory structure Useful UNIX Linux commands Process concept attributes states types CPU- and I O-bound PCB OS queues CPU scheduling and context switch 28 April 2022 Copyright Virtual University of Pakistan Schedulers Long term scheduler Short term scheduler Medium term scheduler 28 April 2022 Copyright Virtual University of Pakistan Queues in a Computer System 28 April 2022 Copyright Virtual University of Pakistan Long Term Scheduler Long-term scheduler or job scheduler selects processes from the job pool to be brought into the ready queue. Long-term scheduler is invoked very infrequently seconds minutes may be slow . The long-term scheduler controls the degree of multiprogramming. More processes smaller percentage of time each process is executed 28 April 2022 Copyright Virtual University of Pakistan Short Term Scheduler Short-term scheduler or CPU scheduler selects which process should be executed next and allocates it the CPU through the dispatcher. Short-term scheduler is invoked very frequently milliseconds must be fast . Invoked when following events occur CPU slice of the current process finishes Current process needs to wait for an event Clock interrupt I O interrupt System call 28 April 2022 Copyright Virtual University of Signal Pakistan Medium Term Scheduler Also known as swapper Selects an in-memory process and swaps it out to the disk temporarily Swapping decision is based on several factors Arrival of a higher priority process but no memory available Poor mix of jobs 2022 28 April Memory request of Virtual Copyright a process University of cannot be met Pakistan Addition of Medium Term Scheduling 28 April 2022 Copyright .