In this chapter, we discuss various ways to manage memory. The memory- management algorithms vary from a primitive bare-machine approach to paging and segmentation strategies. Each approach has its own advantages and disadvantages. Selection of a memory-management method for a specific system depends on many factors, especially on the hardware design of the system. As we shall see, many algorithms require hardware support, leading many systems to have closely integrated hardware and operating-system memory management. | CSC 322 Operating Systems Concepts Lecture - 10: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-2) Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 2 One CPU and many process to run (Multiprogramming) A choice is to be made that which process to run next! Usually many processes in ready state Ready to run on CPU Focus on a single CPU here Need strategies for Allocating CPU time (time quantum) Selecting next process to run Deciding what happens after a process completes a system call, or completes I/O Short-term scheduling Must not take much CPU time to do the scheduling CPU Scheduling Lecture-10 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Draw this Figure on the board so that we can use it on slide #3 when I’m talking about when process scheduling occurs. Ahmed Mumtaz Mustehsan, CIIT, Islamabad Scheduler and Scheduling Algorithms The part of | CSC 322 Operating Systems Concepts Lecture - 10: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-2) Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 2 One CPU and many process to run (Multiprogramming) A choice is to be made that which process to run next! Usually many processes in ready state Ready to run on CPU Focus on a single CPU here Need strategies for Allocating CPU time (time quantum) Selecting next process to run Deciding what happens after a process completes a system call, or completes I/O Short-term scheduling Must not take much CPU time to do the scheduling CPU Scheduling Lecture-10 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Draw this Figure on the board so that we can use it on slide #3 when I’m talking about when process scheduling occurs. Ahmed Mumtaz Mustehsan, CIIT, Islamabad Scheduler and Scheduling Algorithms The part of the operating system that makes the choice that which process to run next is called the scheduler. The algorithm used by scheduler is called the scheduling algorithm. Note: Generally the issues that apply to process scheduling also apply to thread scheduling. Personal Computer User One user who only competes with himself for the CPU Computers have gotten so much faster over the years that the CPU is not a limited resource any more. Hardly any scheduling is required. Scheduling algorithm – Does not Matter For Lecture-10 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 4 Batch servers; Carry out background processing computing insurance claim Time sharing machines; serving interactive users Networked servers; sharing resources You care if you have a bunch of users and/or if the demands of the jobs differ from process to process (I/O bound jobs and CPU bound jobs) Scheduling algorithms – Do Matter For Lecture-10 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 5 Bursts of CPU usage alternate with periods .
