©j.tiberghien - ulb-vub version 2007 première partie, chap. 2, page 1 chapitre 1.2 systèmes...

©J.Tiberghien - ULB-VUBVersion 2007 1Première partie, chap. 2, page

Chapitre 1.2

Systèmes d’exploitation

©J.Tiberghien - ULB-VUBVersion 2007 2Première partie, chap. 2, page

Layered Operating System model

Hardware

Operating

SystemApplication

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Absolute Binary Loader

ABL

CentralMemory

s3,t4

s3,t4

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Command Interpreter

ABL

CentralMemory

chess

s3,t4

Cmnd.Int.

Fmgr.

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Interactive usage

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Batch Processing

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File Manager

• Organizes data on disk

• Hides the details of physical files

• Offers standardized file organizations– Sequential– Random Access– Indexed Sequential

• Maintains File Directories

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Random Access Files

• Space inefficient• Fast access

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Sequential Files

• Space efficient• Slow access

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Indexed Sequential Files

Good compromise:•Space efficient•Access reasonably fast

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Command Interpreter

ABL

chess

Cmnd.Int.

Fmgr.

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Control by Command Interpreter

Program X

Return to CMND.INT

Start User Pgm

Cmnd Interpreter

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Interrupts

Interrupt Handler

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KFL =

KDA =DDA =

4 5 6

1 2 3

* 0 #

7 8 9

Data Memory

Arithmetic Unit

Control Unit

Program Memory

ND =

SC =

p1 COPY #0 ND P2

p2 COPY #0 SC P3

p3 NE? ND #3 P3 P4

p4 NE? SC #321 P1 P5

p5 COPY #1 DDA P1

p10 MUL SC #10 SC P11p11 ADD SC KDA SC P12

p13 ADD ND #1 ND P14p12 COPY #0 KFL P13

Interrupt handler

p14 RTI

Interrupt

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Interrupt Handler

Program X

Return to int.handlr

Start User Pgm

Interrupt Handler

Find cause int.

ControlUnit

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Interrupt Handler Based System

Commandinterpreter

Userprogram

Filemanager

A.B.L.

Interrupthandler

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Single-task Systems

active

waitingfor cpu

Blocked(= busywaiting)

task completed

start I/O

activation

load

I/Ocompletion

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active

waitingfor cpu blocked

task completed

start I/Opreemption

activation

load

swapout

I/Ocompletion(interrupt)

Multi-task Systems

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Multitasking Issues• Process Scheduling

Which program becomes active when ?

• Job Scheduling (or Queue Management)Which programs reside in Central Memory ?

• Memory ManagementHow much memory gets each program ?

• Output SpoolingHow to keep output of programs apart ?

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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.

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Process Priorities

active

blocked

+1-1

p = p0 waitingfor cpu

+1

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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

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Round Robin

Centralmemory

Preempted tasks

after t seconds

New tasks

Input queue

Completed

tasks

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Memory Management

• Allocates memory to each program

– Static Allocation

• Good Job Scheduling mandatory.

–Dynamic Allocation: Virtual Memory

• Job Scheduling not so important.

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Virtual Memory

Page Table

123

456

cm

pm

pmpm

004

002

10031004

1007

1009

CM PM

cmpm

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Output Spooling

Program A

Program B

Program C

Program D