©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


Layered Operating System model

Hardware

Operating

SystemApplication


Absolute Binary Loader

ABL

CentralMemory

s3,t4

s3,t4


Command Interpreter

ABL

CentralMemory

chess

s3,t4

Cmnd.Int.

Fmgr.


Interactive usage


Batch Processing


File Manager

• Organizes data on disk

• Hides the details of physical files

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

• Maintains File Directories


Random Access Files

• Space inefficient• Fast access


Sequential Files

• Space efficient• Slow access


Indexed Sequential Files

Good compromise:•Space efficient•Access reasonably fast


Command Interpreter

ABL

chess

Cmnd.Int.

Fmgr.


Control by Command Interpreter

Program X

Return to CMND.INT

Start User Pgm

Cmnd Interpreter


Interrupts

Interrupt Handler


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


Interrupt Handler

Program X

Return to int.handlr

Start User Pgm

Interrupt Handler

Find cause int.

ControlUnit


Interrupt Handler Based System

Commandinterpreter

Userprogram

Filemanager

A.B.L.

Interrupthandler


Single-task Systems

active

waitingfor cpu

Blocked(= busywaiting)

task completed

start I/O

activation

load

I/Ocompletion


active

waitingfor cpu blocked

task completed

start I/Opreemption

activation

load

swapout

I/Ocompletion(interrupt)

Multi-task Systems


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 ?


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.


Process Priorities

active

blocked

+1-1

p = p0 waitingfor cpu

+1


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


Round Robin

Centralmemory

Preempted tasks

after t seconds

New tasks

Input queue

Completed

tasks


Memory Management

• Allocates memory to each program

– Static Allocation

• Good Job Scheduling mandatory.

–Dynamic Allocation: Virtual Memory

• Job Scheduling not so important.


Virtual Memory

Page Table

123

456

cm

pm

pmpm

004

002

10031004

1007

1009

CM PM

cmpm


Output Spooling

Program A

Program B

Program C

Program D

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

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