©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 1 Chapitre 1.2 Systèmes dexploitation

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 2 Layered Operating System model Hardware Operating System Application

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 3 Absolute Binary Loader ABL Central Memory s3,t4

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 4 Command Interpreter ABL Central Memory chess s3,t4 Cmnd.Int. Fmgr.

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 5 Interactive usage

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 6 Batch Processing

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 7 File Manager Organizes data on disk Hides the details of physical files Offers standardized file organizations –Sequential –Random Access –Indexed Sequential Maintains File Directories

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 8 Random Access Files Space inefficient Fast access

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 9 Sequential Files Space efficient Slow access

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 10 Indexed Sequential Files Good compromise: Space efficient Access reasonably fast

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 11 Command Interpreter ABL chess Cmnd.Int. Fmgr.

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 12 Control by Command Interpreter Program X Return to CMND.INT Start User Pgm Cmnd Interpreter

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 13 Interrupts Interrupt Handler

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 14 KFL = KDA = DDA = *0# 789 Data Memory Arithmetic Unit Control Unit Program Memory ND = SC = p1 COPY #0NDP2 p2 COPY #0SCP3 p3 NE? ND#3P3P4 p4 NE? SC#321P1P5 p5 COPY #1DDAP1 p10 MUL SC#10SCP11 p11ADDSCKDASCP12 p13 ADD ND#1NDP14 p12 COPY #0KFLP13 Interrupt handler p14 RTI Interrupt

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 15 Interrupt Handler Program X Return to int.handlr Start User Pgm Interrupt Handler Find cause int. Control Unit

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 16 Interrupt Handler Based System Command interpreter User program File manager A.B.L. Interrupt handler

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 17 Single-task Systems active waiting for cpu Blocked (= busy waiting) task completed start I/O activation load I/O completion

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 18 active waiting for cpu blocked task completed start I/O preemption activation load swap out I/O completion (interrupt) Multi-task Systems

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 19 Multitasking Issues Process Scheduling Which program becomes active when ? Job Scheduling (or Queue Management) Which programs reside in Central Memory ? Memory Management How much memory gets each program ? Output Spooling How to keep output of programs apart ?

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 20 Process Scheduler All programs have a priority and the one waiting with the highest priority becomes active. Non-preemptive Scheduling: Priorities are compared whenever the active program blocks itself a clock tick occurs (typically every 10 mS) Preemptive Scheduling Priorities are continuously compared.

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 21 Process Priorities active blocked +1 p = p 0 waiting for cpu +1

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 22 Job Scheduler Selects the programs to be loaded in Central Memory Manual selection (starting an application under Windows) Automatic selection –based on priorities –Based on the Round Robin algorithm

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 23 Round Robin Central memory Preempted tasks after t seconds New tasks Input queue Completed tasks

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 24 Memory Management Allocates memory to each program –Static Allocation Good Job Scheduling mandatory. –Dynamic Allocation: Virtual Memory Job Scheduling not so important.

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 25 Virtual Memory Page Table cm pm CMPM cm pm

©J.Tiberghien - ULB-VUB Version 2007 Première partie, chap. 2, page 26 Output Spooling Program AProgram BProgram CProgram D