Operating Systems - Introduction - Stephan Sigg · Introduction 1 De nition of operating systems 2 A condensed history of operating systems 3 Operating system basics The computer

Operating SystemsIntroduction

Stephan Sigg

Distributed and Ubiquitous SystemsTechnische Universitat Braunschweig

November 9, 2010

Stephan Sigg Operating Systems 1/66

Overview and Structure

Introduction to operating systemsHistoryArchitectures

ProcessesProcesses, threads and interprocess communicationProcess scheduling and deadlocks

Memory managementPagingSegmentation

Filesystems

Security and Protection

Distributed systems

Cryptography


OrganisationOrganisation

Participate !

Participation during lecture and exercises to improvecomprehension

Opportunities:

Interactive lecture and exercise: Participate!Solve the exercises in advance

(you will understand the problems better and detect thingsthat you did not understand)

Present your solutionPresent a short Wrap-Up (ca. 5 min.) of the last lectureParticipate in the summary of the current lecture (at the endof the lecture)


OutlineIntroduction

1 Definition of operating systems

2 A condensed history of operating systems

3 Operating system basicsThe computer systemOperating system structureUser mode and kernel modeArchitectures of operating systems

4 Summary


What is an operating system?Definition of operating systems

What is an operating system?



Operating system

”Ein Computer ist, wenn er genau betrachtet wird, nur eineAnsammlung von Plastik und Metall, das zur Leitung von Strombenotigt wird. Dieser ’Industriemull’ kann somit nichtausschliesslich das sein, was wir unter einem modernen Computerverstehen, etwas, das dem Computer ’Leben’ einhaucht und ihn zudem Werkzeug unseres Jahrhunderts macht. Es ist dasBetriebssystem, das die Kontrolle uber das Plastik und Metall(Hardware) ubernimmt und anderen Softwareprogrammen (Excel,Word, . . . ) eine standardisierte Arbeitsplattform (Windows,Unix, OS/2) schafft.”a

aEwert et al., Literatur zu ’Freehand 10’



Definition

Programmbundel, das die Bedienung eines Computers ermoglicht.a

aUniversalworterbuch Rechtschreibung

Definition

Summe derjenigen Programme, die als residenter Teil einerEDV-Anlage fur den Betrieb der Anlage und fur die Ausfuhrungder Anwenderprogramme erforderlich ista

aLexikon der Informatik



Definition

Die Programme eines digitalen Rechensystems, die zusammen mitden Eigenschaften der Rechenanlage die Grundlage der moglichenBetriebsarten des digitalen Rechensystems bilden und insbsonderedie Abwicklung von Programmen steuern und uberwachen.a

aDIN 44300

Definition

Ein Programm das als Vermittler zwischen Rechnerbenutzer undRechnerhardware fungiert. Der Sinn des Betriebssystems ist eineUmgebung bereitzustellen, in der Benutzer bequem und effizientProgramme ausfuhren konnen.a

aA. Silberschatz et al. Operating system concepts, Wiley, 2004.



Definition

Eine Softwareschicht, die alle Teile des Systems verwaltet und demBenutzer eine Schnittstelle oder virtuelle Maschine anbietet, dieleichter zu verstehen und zu programmieren ista

aA. Tanenbaum, Modern operating systems, 3rd edition, Prentice Hall,2008.



Functions of an operating system

An operating system basically performs a set of unrelatedfunctions:

Extending the machine

Managing resources

Providing an environment where multiple programs canexecute


What is an operating system?The operating system as an extended machine

Issue: The architecture of most computers at the machinelevel is primitive and hard to program

Solution: The operating system provides an abstraction layerto ease interaction with the hardware



Example

The floppy disk

Basic commands are read and writeRequire 13 parameters packed into 9 bytesAddress of the disk block, number of sectors per track,recording mode on physical medium, ...Controller chip returns 23 status end error fields (7 bytes)

Programmer must constantly be aware if motor is on or offIf off: switch motor on (long startup delay)Switch off frequently to prevent the disk from wearing out

.Stephan Sigg Operating Systems 12/66


The operating system manages all pieces of a complex system

Provides an orderly and controlled allocation of the processor,memories, and I/O devices among the various programs



Example

Imagine several programs accessing the same physical printersimultaneously.

The output might easily consist of several lines from the firstprint job, then several lines from the next and so on

The operating system has to schedule access to the hardwareamong programs

.


OutlineIntroduction




4 Summary


A condensed history of operating systemsEarly punchcard systems

Punchcards/Lochkarten

Since 1725 Punchcards have been utilised for the stearing ofweaving machines

1890 Herman Hollerith utilises punchcards for a census ofpopulation (Volkszahlung)

until 1970s Utilised as storage media

.Stephan Sigg Operating Systems 16/66

A condensed history of operating systemsFirst universal electronic calculators

ENIAC, 1946US armyCalculation of ballistictables

Size: 10m x 17m x 2.7m

Weight: 27 tons

Performance: 174 kW (> 17000tubes)

Price: 468.000 $

Comp.Power: 500 Additions persecond


A condensed history of operating systemsFirst universal electronic calculators


A condensed history of operating systemsSince 1945: Serial operation

Programming

Machine codeInput via punchcardsOutput via printerErrors indicated by control lights

Minimum CPU utilisation

Much time spent for slow I/Odevices (punchcard reader, printer)

Scheduling of CPU resources onpaper calendars

Waste of resources due to too widetime windows or abort through error

First system software: reusableprogram libraries

Device drivers, Debugger


A condensed history of operating systemsSince 1955: Simple batch systems

Reduce the frequency of manualoperation

First operating systems: residentmonitors

Interpretation of Job controlinstructionsLoad and execution of programsDevice triggering

$FTN

$JOB

$LOAD

$RUN

$END

Fortran code

Control cards (new)

Input data



The monitor stayed in memory whilecontinuously executing applicationprograms

Problems due to application programerrors

Program does not terminateProgram writes to memory area ofmonitorProgram accesses the card readerand interpretes control input as data

Device driver

sequential

job control

Control

interpreter

language

Application

programarea

Memory

Mo

nit

or



Solutions

Timer provides interruptsTraps for erroneous programs

Fence register for primitivememory protection

Supervisor mode (PriviligierterArbeitsmodus) of CPU

Deactivate fence registerIn/Out

Application

programarea

Memory

Interrupt

mechanism

Device driver

sequential

job control

Control

interpreter

language

UnusedM

on

ito

r

02FF

0300

0000

1FFF

0300

registerFence

Timer


A condensed history of operating systemsThe input-/Output- bottleneck

Problem: CPU works faster than card reader

Processing resources wasted by active waiting

Solution 1: Off-line processing

With the help of tape drivesParallel input-/output via several satellite computers

1

1A. Tanenbaum, Modern operating systems, 3rd edition, Prentice Hall, 2008.


A condensed history of operating systemsThe input-/Output- bottleneck

Problem: CPU works faster than card reader

Processing resources wasted by active waiting

Solution 2: SpoolingWith the help of disc drives

Random access (Wahlfreier Zugriff) and Direct MemoryAccess (DMA)Calculations and In-/Output then overlappingRules for CPU allocation

Card reader

Disk

CPU

Printer

Waiting jobs Result data

.


A condensed history of operating systemsSince 1965: Multiple programs simultaneously

Despite spooling a single program utilises the CPU notefficiently

CPU bursts and I/O bursts in which the CPU is idle alternate

With multitasking, the CPU processes several jobs in parallel

CPU

CPU CPU

CPU CPU

CPUCPU

CPUI/O

I/O

I/O I/O

I/O

I/O

Multiprocessing

Program A

Program B

Program A and B

CPU CPUI/O I/O

Single processing

Program A

.



The operating system is gaining complexity

Parallel I/O activities (Nebenlaufigkeit)

Administration of the memory for various programs

Internal administration of executing processes

Scheduling of CPU resources

Multi-user operation (security and accounting)



Memory management

Allocate free memory dynamically

Memory protection

Simple fence register not sufficientto isolate single programsSolution: Simple MemoryManagement Unit (MMU)

Process management

Every process has its own contextExchange context at process change

0000

FFFF

systemOperating

Program B

Program A

Unused

Memory CPU and MMU

Lo

Hi

Context BContext A

Lo

SP

IP

Hi

SP

IP

Lo

Hi

4000

5000

4000

430A

4EEO

5000

F000

62E2

E340

(text, data, bss, stack)

(text, data, bss, stack)

EFFF

3FFF

4000

4FFF

5000

− −

− −

Bounds register

pointerinstruction

stackpointer

5000


A condensed history of operating systemsDialogue driven

New In/Output devices enableinteractive software

Keyboard, Monitor, later mouse

Time-sharing operation

Improved response-time forinteractive usersTiming interrupts suppress longrunning processes

Interactive software development dueto system programs

Editor, shell, compiler, debugger

Disks and file systems allow access ofprograms and data at any time

First Apple Macintosh(January 24, 1984)


A condensed history of operating systemsToday’s operating systems

Microsoft Windows

Evolved from MS-DOS

Proprietary system

Windows Vista:Approximately 50 Mio LOC

Hardware

Kern

el m

od

eHardware Abstraction Layer (HAL)

Object Manager

Executive Services

Executi

ve

User

mod

e

Integral subsystems Environment subsystems

I/OManager

SecurityReferenceMonitor

IPCManager

VirtualMemoryManager(VMM)

ProcessManager

PnPManager

PowerManager

WindowManager

GDI

Work-stationservice

Serverservice

SecurityWin32 POSIX OS/2

Win32Application

POSIXApplication

OS/2Application

Kernel mode drivers Microkernel

Hardware



Minix

Developed by Andrew S.Tanenbaum for teachingpurposes

Less than 4000 LOC

Device driver as programs inuser space

Hardware

Kernel mode

User

mod

e

Device processesDisk TTY Net

Kernel

Hardware

Print Other

Clock task System task

Server processesFile PM Reinc ... Other

User processesShell Make User ... Other



Berkeley Software Distribution (BSD)

Developed at UC Berkeley in 1977

Basis for many further operatingsystems

FreeBSDOpenBSDEarly SunOSMac OS X



Linux

System composed ofapplications, Services,Kernel, Hardware controllers

Kernel presents virtualinterface to user processes

Pure OS-core ca. 1 Mio LOC

Therefore suited forembedded systems

Hardware

Kernel

User level

CPU

Hardware controlersSystem memory terminal

Process Process Process Process process

NICdisk

signals system calls

scheduler

file systemnetwork

driversinterrupts

device

memorytraps/faults

virtual memory

network

protocolsblock

drivers

chardevicedrivers



Mac OS X

Distributed since 2001 byApple for Macintoshcomputers

Successor of NeXTStep andMac OS 9

Based on Darvin (which isitself based on BSD)

Hardware

Cor

e O

S (D

arw

in)

Gui (Aqua)

HardwareM

ach

Ke

rne

l ('

xn

u')

I/O Kit Drivers

BS

D

File SystemsNetworking

POSIXNKE

System utilities

Java

JRE

JVM

AP

I

Application services

Core servicesCore foundation Core services non-GUI-api

Carbon

CoreCarbon

Quartz OpenGL PrintCore

QuickTimeBSD Classic Cocoa



QNX

Developed by Gordon Bell and DanDodge in 1982 for Intel 8088

Real-time operating system

Tiny OS-core holds only CPUscheduler, inter processcommunication, interrupt handlingand timer

Modular system

Mainly embedded systems(Automobile, Router)

Proprietary system


OutlineIntroduction




4 Summary


Operating system basicsIntroduction

To understand the operation of operating systems, somebackground in

I/OComputer ArchitectureStorage conceptsNetworking

is required


Operating system basicsThe computer system

Computer system operation

A general purpose computer system consists of

One or more CPUsA number of device controllersShared memoryconnected through a common bus

CPUdisk

controllerUSB

controllergraphicsadapter

memory




CPU and device controllers can execute concurrently andcompete for the memory

A memory controller synchronises the memory access

CPUdisk

controllerUSB


memory




When started, a computer requires an initial program to run

bootstrap programSimple ’firmware’Typically stored in read-only memory (ROM) or Electricallyerasable programmable read-only memory (EEPROM)Initialises all aspects of the system, e.g.

CPU registersDevice controllersMemory contents

Loads and starts operating system

Loads into memory the operating system kernel

Starts the first process of the system

Waits for events to occur



Storage structure

The CPU can load instructions only from memory

Any executable programs have to be loaded into memory

Memory provides an array of words

Each word has its own address

Interaction through sequence of load or store instructions

Load moves a word from memory to register within the CPUStore moves the content of a register to main memory

Load

Store

Load executableprograms into

memory



Storage structure

A typical von Neumann-execution cycle:1 Fetch an instruction from memory2 Store that instruction into the instruction register3 Decode instruction (probably fetch operands from memory)4 Execution5 Result may be written back to memory

1: Fetch

5: Write back

2: Store to IR

3: D

ecod

e

3: execute



22Hennessey and Patterson, Computer Architecture: A quantitative

approach, Morgan Kaufmann, 2002Stephan Sigg Operating Systems 42/66


33Hennessey and Patterson, Computer Architecture: A quantitative

approach, Morgan Kaufmann, 2002Stephan Sigg Operating Systems 43/66


Storage structure

Since access to main memory is fast, we naturally want allprograms and data to reside there

This is typically not possible, since1 Main memory is usually too small2 Main memory is a volatile storage device that loses its content

after power is turned off

Therefore: Secondary storage is required as extension

?Stephan Sigg Operating Systems 44/66


Semi

cond

uctor

mem

ory Registers

Cache

Main memory

Electronic disk

Magnetic disk

Optical disk

Magnetic tapes

fast

slowch

eap

expensiv

e

cost

access

expensiv

e



I/O structure

Large portion of OS-code is dedicated to managing I/O

Typically, multiple device controllers connected to CPU over acommon bus

Each device controller is in charge of a specific type of device

CPUdisk

controllerUSB


memory



I/O structure

A device controller maintains

Local buffer storageSome special purpose register

Moves data between devices and its local buffer storage

OS has device driver for each device controller

Driver presents a uniform inferface to the operating system

CPUdisk

controllerUSB


memory



I/O structure

To start an I/O operation

Driver loads appropriate registers within device controllerController examines their contents to obtain action to takeController starts data transfer from device to its local bufferWhen transfer is complete, controller informs the driverDevice driver then returns control to the operating system

CPUdisk

controllerUSB


memory



I/O structure

This form of interrupt-driven operation is not feasible forgreater amounts of data

Solution: Direct Memory Access (DMA)

Device controller transfers entire block of data directly to orfrom its own buffer storage to memoryCPU available during this time

CPUdisk

controllerUSB


memory


Operating system basicsOperating system structure

Memory management

OS provides environment within whichprograms are executed

Execution quasi parallel

OS keeps several programs inmemory simultaneouslySchedules these for their CPU timeWhen programs are idle (e.g. due toI/O operation), they are temporaryremoved from memoryOther programs can then beexecuted instead

MemoryOperating

system

Program 1

Program 2

Program 3

Program 4


Operating system basicsOperating system structure

Operating system operations

In order to ensure proper execution of the operating systemwe distinguish between

Kernel modeUser mode

For each operation a bit is added to the hardware of thecomputer that indicates user mode or kernel mode

Potentially harmful operations executed only in kernel mode

Usermode

Kernelmode

User process Callsystem call

Executesystem call

Return fromsystem call

mod

e b

it = 0

mode b

it =

1Stephan Sigg Operating Systems 51/66

User mode and kernel modeCPU-modi

Separation of operating system process and application processes

Protection of the operating system from software failures

Trend: Outplacement of parts of the operating system (e.g.driver)

Switch between user mode and kernel mode

CHM (Change Mode) Operation (only privileged processes)

Events: Interrupts or Traps

Usermode

Kernelmode

User process Callsystem call

Executesystem call

Return fromsystem call

mod

e b

it = 0

mode b

it =



User mode

Processor processes instructionsof application programs

Instruction set of processorrestricted to subset(unprivileged instruction set)

Hardware access restricted(hardware protection)

Direct access to executingprograms forbidden

Usermode User process Call

system callReturn fromsystem call

mode bit =

0 mod

e bi

t =



Kernel mode

Processor processes instructions ofthe operating system

Complete instruction set available(privileged instruction set)

Direct, unrestricted access tohardware

Manipulation of internal data fromrunning processes possible

Errors compromise system stability

Kernelmode Execute

system call

mode bit =

0

mod

e bi

t =


Entry points to an operating systemTraps

System calls, supervisor calls, software traps

Synchronous to running application (e.g.count=read(file,buffer,size))

Parameter forwarded via register, stack or parameter block

Hardware traps

Synchronous to running applications

OS forwards errors to application responsible for it


Entry points to an operating systemInterrupts

Hardware interrupts

Asynchronous with running application

E.g. Receiving of bit-sequence on modem

Software interrupts

Asynchronous to running application

Often created internally to shift sophisticated calculation tolower priority processes

Asynchronous interrupts can interrupt system calls and otheroperating system processes


Entry points to an operating systemInterrupts and I/O

Program flow typically not reproducible

Interrupts depend on environmental conditions

Processes should not be implemented under timingassumptions

I/O-devices can work in parallel with the CPU

Goal: Keep all devices and CPU busy most of the time

Typical strategy: Higher priority for I/O-intensive tasks


Architectures of operating systemsOperating system architectures

We distinguish between

Monolithic architecturesLayered architectures

Hardware

Hardware


Architectures of operating systemsLayered architectures

Layers to control complexity

Increased flexibility

Often overhead to control interoperation among layers

Hardware

Syst

em

prog

ram

sH

ardw

are

Physical devices

Microarchitecture

Machine language

Operating system

Compilers Editors Command interpreter

prog

ram

sAp

plica

tion

Banking system

AirlineReservation

Web browser



OS consists of several layers

Higher layers provide new functionality

Modular structure improves error detection and qualitymanagement

Strict satisfaction of layers increases overhead

Hardware

Syst

em

prog

ram

sHa

rdwa

re

Physical devices

Microarchitecture

Machine language

Operating system

Compilers Editors Command interpreter

progra

msAp

plicati

on

Banking system

AirlineReservation

Web browser



Layers to control complexity

Increased flexibility

Often overhead to control interoperation among layers

Hardware

Service procedures

Main procedure

Utility procedures



OS as set of procedures and functions without structure

Every procedure can call arbitrary other procedures

Functions that realise subfunction of OS are grouped

Hardware

Service procedures

Main procedure

Utility procedures


OutlineSummary




4 Summary


Introduction to operating systemsQuestions, discussion, remarks

Questions?


OrganisationOrganisation

Participate !

Participation during lecture and exercises to improvecomprehension

Opportunities:

Interactive lecture and exercise: Participate!Solve the exercises in advance

(you will understand the problems better and detect thingsthat you did not understand)

Present your solutionPresent a short Wrap-Up (ca. 5 min.) of the last lectureParticipate in the summary of the current lecture (at the endof the lecture)


LiteratureRecommended literature

A. Tanenbaum, Moderne Betriebssysteme, 2nd edition,Prentice Hall, 2009.

A. Tanenbaum, Modern operating systems, 3rd edition,Prentice Hall, 2008.

A. Silberschatz et al. Operating system concepts, Wiley, 2004.

W. Stallings, Operating systems, 6th edition, Prentice Hall,2008.


Documents

Operating Systems - Introduction - Stephan Sigg · Introduction 1 De nition of operating systems 2 A condensed history of operating systems 3 Operating system basics The computer