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Chapter 1: Introduction

CS-206 – Operating Systems



2

Objectives

To describe the basic organization of computer systems To provide a grand tour of the major components of

operating systems

To give an overview of the many types of computing

environments

To explore several open-source operating systems



!hat is an Operating System"

A program that acts as an intermediary between auser of a computer and the computer hardware

Operating system goals:

Execute user programs and mae solving user

problems easier

!ae the computer system convenient to use

"se the computer hardware in an efficient manner



#

Computer System Structure

#omputer system can be divided into four components:

$ardware % provides basic computing resources

#&"' memory' ()O devices

Operating system

#ontrols and coordinates use of hardware among various

applications and users

Application programs % define the ways in which the system

resources are used to solve the computing problems of the users

*ord processors' compilers' web browsers' database systems'

video games

"sers

&eople' machines' other computers



$

%our Components o& a Computer System



6

!hat Operating Systems 'o

+epends on the point of view

"sers want convenience' ease o& use and good per&ormance

+on,t care about resource uti(i)ation

ut shared computer such as main&rame or minicomputer must

eep all users happy

"sers of dedicate systems such as *or+stations have dedicated

resources but fre.uently use shared resources from servers

$andheld computers are resource poor' optimized for usability

and battery life

/ome computers have little or no user interface' such asembedded computers in devices and automobiles


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Operating System 'e&inition

O/ is a resource a((ocator

!anages all resources

+ecides between conflicting re.uests for efficient and

fair resource use O/ is a contro( program

#ontrols execution of programs to prevent errors and

improper use of the computer



Operating System 'e&inition .Cont/

0o universally accepted definition

1Everything a vendor ships when you order an operating

system2 is a good approximation

ut varies wildly

1The one program running at all times on the computer2

is the +erne(3

Everything else is either

a system program 4ships with the operating system5 'or

an application program3



Computer Startup

bootstrap program is loaded at power-up or reboot Typically stored in 6O! or E&6O!' generally

nown as &irm*are

(nitializes all aspects of system

7oads operating system ernel and starts execution



Computer System Organi)ation

#omputer-system operation

One or more #&"s' device controllers connect through common bus

providing access to shared memory

#oncurrent execution of #&"s and devices competing for memory

cycles



ead 3 !rite

4emory

#loc #ycle #&"

!emory #ycle

!emory unit

8k x m

m 'ata input

m 'ata output

k 5ddress



Computer-System Operation

()O devices and the #&" can execute concurrently Each device controller is in charge of a particular device

type

Each device controller has a local buffer

#&" moves data from)to main memory to)from local

buffers

()O is from the device to local buffer of controller

+evice controller informs #&" that it has finished itsoperation by causing an interrupt



Common %unctions o& Interrupts

(nterrupt transfers control to the interrupt serviceroutine generally' through the interrupt vector' which

contains the addresses of all the service routines

(nterrupt architecture must save the address of the

interrupted instruction A trap or eception is a software-generated interrupt

caused either by an error or a user re.uest

An operating system is interrupt driven


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Interrupt 7ector 8ab(e 4echanism


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Interrupt 9and(ing

The operating system preserves the state of the #&" bystoring registers and the program counter

+etermines which type of interrupt has occurred:

po((ing

vectored interrupt system

/eparate segments of code determine what action should

be taen for each type of interrupt



Interrupt 8ime(ine


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I3O Structure

After ()O starts' control returns to user program only upon ()Ocompletion

*ait instruction idles the #&" until the next interrupt

*ait loop 4contention for memory access5

At most one ()O re.uest is outstanding at a time' no simultaneous()O processing

After ()O starts' control returns to user program without waiting for ()Ocompletion

System ca(( % re.uest to the O/ to allow user to wait for ()Ocompletion

'evice-status tab(e contains entry for each ()O device indicatingits type' address' and state

O/ indexes into ()O device table to determine device status and tomodify table entry to include interrupt



Storage 'e&initions and otation evie*

The basic unit of computer storage is the bit. A bit can contain one of two

values, 0 and 1. All other storage in a computer is based on collections of bits.Given enough bits, it is amazing how many things a computer can represent:numbers, letters, images, movies, sounds, documents, and programs, to namea few. A byte is bits, and on most computers it is the smallest convenientchun! of storage. "or e#ample, most computers don$t have an instruction tomove a bit but do have one to move a byte. A less common term is word,which is a given computer architecture$s native unit of data. A word is made upof one or more bytes. "or e#ample, a computer that has %&'bit registers and

%&'bit memory addressing typically has %&'bit ('byte) words. A computere#ecutes many operations in its native word size rather than a byte at a time.

*omputer storage, along with most computer throughput, is generallymeasured and manipulated in bytes and collections of bytes.A kilobyte, or KB, is 1,0+& bytesa megabyte, or MB, is 1,0+&+ bytes

a gigabyte, or GB, is 1,0+&

bytesa terabyte, or TB, is 1,0+&& bytesa petabyte, or PB, is 1,0+&- bytes

*omputer manufacturers often round off these numbers and say that amegabyte is 1 million bytes and a gigabyte is 1 billion bytes. etwor!ingmeasurements are an e#ception to this general rule/ they are given in bits(because networ!s move data a bit at a time).



Storage Structure

!ain memory % only large storage media that the #&" can access directly

andom access

Typically vo(ati(e

/econdary storage % extension of main memory that provides large

nonvo(ati(e storage capacity

$ard diss % rigid metal or glass platters covered with magnetic recording

material

+is surface is logically divided into trac+s' which are subdivided into sectors

The dis+ contro((er determines the logical interaction between the device and

the computer

So(id-state dis+s % faster than hard diss' nonvolatile

9arious technologies

ecoming more popular



Storage 9ierarchy

/torage systems organized in hierarchy /peed

#ost

9olatility

Caching % copying information into faster storage system

main memory can be viewed as a cache for secondary

storage

'evice 'river for each device controller to manage ()O

&rovides uniform interface between controller and

ernel



Storage-'evice 9ierarchy



Caching

(mportant principle' performed at many levels in a computer

4in hardware' operating system' software5

(nformation in use copied from slower to faster storage

temporarily

;aster storage 4cache5 checed first to determine ifinformation is there

(f it is' information used directly from the cache 4fast5

(f not' data copied to cache and used there

#ache smaller than storage being cached

#ache management important design problem

#ache size and replacement policy



2

'irect 4emory 5ccess Structure

"sed for high-speed ()O devices able to transmitinformation at close to memory speeds

+evice controller transfers blocs of data from buffer

storage directly to main memory without #&"

intervention Only one interrupt is generated per bloc' rather than the

one interrupt per byte



2#

9o* a 4odern Computer !or+s

A von Neumann architecture



2$

Computer-System 5rchitecture

!ost systems use a single general-purpose processor

!ost systems have special-purpose processors as well

4u(tiprocessors systems growing in use and importance

Also nown as para((e( systems' tight(y-coup(ed systems

Advantages include:

1/ Increased throughput

2/ ;conomy o& sca(e

/ Increased re(iabi(ity % graceful degradation or fault tolerance

Two types:

1/ 5symmetric 4u(tiprocessing % each processor is assigned a

specific tas3

2/ Symmetric 4u(tiprocessing % each processor performs all tass



26

Symmetric 4u(tiprocessing 5rchitecture



2,

5 'ua(-Core 'esign

!ulti-chip and mu(ticore

/ystems containing all chips

#hassis containing multiple separate systems



2

C(ustered Systems

7ie multiprocessor systems' but multiple systems woring together

"sually sharing storage via a storage-area net*or+ .S5

&rovides a high-avai(abi(ity service which survives failures

5symmetric c(ustering has one machine in hot-standby mode

Symmetric c(ustering has multiple nodes running applications'

monitoring each other

/ome clusters are for high-per&ormance computing .9<C

Applications must be written to use para((e(i)ation

/ome have distributed (oc+ manager 4'=45 to avoid conflicting

operations



2

C(ustered Systems



0

Operating System Structure

4u(tiprogramming 4>atch system5 needed forefficiency

/ingle user cannot eep #&" and ()O devices busy at alltimes

!ultiprogramming organizes jobs 4code and data5 so#&" always has one to execute

A subset of total jobs in system is ept in memory

One job selected and run via job schedu(ing

*hen it has to wait 4for ()O for example5' O/ switchesto another job



1

Operating System Structure

8imesharing 4mu(titas+ing5 is logical extension in which #&"switches jobs so fre.uently that users can interact with each job while

it is running' creating interactive computing

esponse time should be < = second

Each user has at least one program executing in memory process

(f several jobs ready to run at the same time C<? schedu(ing

(f processes don,t fit in memory' s*apping moves them in andout to run

7irtua( memory allows execution of processes not completely

in memory



2

4emory =ayout &or 4u(tiprogrammed System



Operating-System Operations

Interrupt driven 4hardware and software5

$ardware interrupt by one of the devices

/oftware interrupt 4eception or trap:

/oftware error 4e3g3' division by zero5

6e.uest for operating system serviceOther process problems include infinite loop' processes modifying each other or theoperating system



#

Operating-System Operations .cont/

'ua(-mode operation allows O/ to protect itself and othersystem components

?ser mode and +erne( mode

4ode bit provided by hardware

&rovides ability to distinguish when system is runninguser code or ernel code

/ome instructions designated as privi(eged' onlyexecutable in ernel mode

/ystem call changes mode to ernel' return from callresets it to user

(ncreasingly #&"s support multi-mode operations

i3e3 virtua( machine manager 47445 mode for guest 74s



$

8ransition &rom ?ser to @erne( 4ode

Timer to prevent infinite loop ) process hogging resources

Timer is set to interrupt the computer after some time period

>eep a counter that is decremented by the physical cloc3

Operating system set the counter 4privileged instruction5

*hen counter zero generate an interrupt

/et up before scheduling process to regain control or terminate

program that exceeds allotted time



6

<rocess 4anagement

A process is a program in execution3 (t is a unit of wor within thesystem3 &rogram is a passive entity' process is an active entity3

&rocess needs resources to accomplish its tas

#&"' memory' ()O' files

(nitialization data

&rocess termination re.uires reclaim of any reusable resources

/ingle-threaded process has one program counter specifying location ofnext instruction to execute

&rocess executes instructions se.uentially' one at a time' untilcompletion

!ulti-threaded process has one program counter per thread

Typically system has many processes' some user' some operating systemrunning concurrently on one or more #&"s

#oncurrency by multiplexing the #&"s among the processes ) threads



,

<rocess 4anagement 5ctivities

The operating system is responsible for the following activities

in connection with process management:

#reating and deleting both user and system processes

/uspending and resuming processes

&roviding mechanisms for process synchronization

&roviding mechanisms for process communication

&roviding mechanisms for deadloc handling



4emory 4anagement

To execute a program all 4or part5 of the instructions must be in

memory

All 4or part5 of the data that is needed by the program must be in

memory3

!emory management determines what is in memory and when

Optimizing #&" utilization and computer response to users

!emory management activities

>eeping trac of which parts of memory are currently being used

and by whom

+eciding which processes 4or parts thereof5 and data to move intoand out of memory

Allocating and deallocating memory space as needed



Storage 4anagement

O/ provides uniform' logical view of information storage

Abstracts physical properties to logical storage unit - &i(e Each medium is controlled by device 4i3e3' dis drive' tape drive5

9arying properties include access speed' capacity' data-transferrate' access method 4se.uential or random5

;ile-/ystem management

;iles usually organized into directories

Access control on most systems to determine who can access what

O/ activities include

#reating and deleting files and directories

&rimitives to manipulate files and directories!apping files onto secondary storage

acup files onto stable 4non-volatile5 storage media



#0

4ass-Storage 4anagement

"sually diss used to store data that does not fit in main memory or data that

must be ept for a 1long2 period of time

&roper management is of central importance

Entire speed of computer operation hinges on dis subsystem and its

algorithms

O/ activities

;ree-space management

/torage allocation

+is scheduling

/ome storage need not be fast

Tertiary storage includes optical storage' magnetic tape

/till must be managed % by O/ or applications

9aries between *O6! 4write-once' read-many-times5 and 6* 4read-

write5



#1

<er&ormance o& 7arious =eve(s o& Storage

!ovement between levels of storage hierarchy can be explicit or implicit



#2

4igration o& data A5B &rom 'is+ to egister

!ultitasing environments must be careful to use most recent value' no

matter where it is stored in the storage hierarchy

!ultiprocessor environment must provide cache coherency in hardware

such that all #&"s have the most recent value in their cache

+istributed environment situation even more complex

/everal copies of a datum can exist

9arious solutions covered in #hapter =?



#

I3O Subsystem

One purpose of O/ is to hide peculiarities of hardware devices from the

user ()O subsystem responsible for

!emory management of ()O including buffering 4storing data

temporarily while it is being transferred5' caching 4storing parts of

data in faster storage for performance5' spooling 4the overlapping of

output of one job with input of other jobs5 @eneral device-driver interface

+rivers for specific hardware devices

i S i



##

<rotection and Security

<rotection % any mechanism for controlling access of processes or users to

resources defined by the O/ Security % defense of the system against internal and external attacs

$uge range' including denial-of-service' worms' viruses' identity theft'theft of service

/ystems generally first distinguish among users' to determine who can do

what "ser identities 4user I's' security (+s5 include name and associated

number' one per user

"ser (+ then associated with all files' processes of that user to determineaccess control

@roup identifier 4group I'5 allows set of users to be defined andcontrols managed' then also associated with each process' file

<rivi(ege esca(ation allows user to change to effective (+ with morerights

@ ( ' S



#$

@erne( 'ata Structures

!any similar to standard programming data structures

Singly linked list

Doubly linked list

Circular linked list

S



#6


>inary search tree

left < right

/earch performance is O(n)

>a(anced binary search tree is O(lg n)

@ ( ' S



#,


9ash &unction can create a hash map

>itmap % string of n binary digits representing the status of n items

7inux data structures defined in include files <linux/list.h>, <linux/kfifo.h>,

<linux/rbtree.h>

C ti ; i t 8 diti (



#

Computing ;nvironments - 8raditiona(

/tand-alone general purpose machines

ut blurred as most systems interconnect with others

4i3e3' the (nternet5

<orta(s provide web access to internal systems

et*or+ computers 4thin c(ients5 are lie *ebterminals

!obile computers interconnect via *ire(ess net*or+s

0etworing becoming ubi.uitous % even home systems

use &ire*a((s to protect home computers from (nternetattacs

C ti ; i t 4 bi(



#

Computing ;nvironments - 4obi(e

$andheld smartphones' tablets' etc

*hat is the functional difference between them and a

1traditional2 laptopB

Extra feature % more O/ features 4@&/' gyroscope5

Allows new types of apps lie augmented reality "se (EEE CD83== wireless' or cellular data networs for

connectivity

7eaders are 5pp(e iOS and oog(e 5ndroid

C ti ; i t 'i t ib t d



$0

Computing ;nvironments – 'istributed

+istributed computiing

#ollection of separate' possibly heterogeneous' systems networedtogether

et*or+ is a communications path' 8C<3I< most common

% =oca( 5rea et*or+ 4=55

% !ide 5rea et*or+ 4!55

% 4etropo(itan 5rea et*or+ 4455

% <ersona( 5rea et*or+ 4<55

et*or+ Operating System provides features between systems across

networ

#ommunication scheme allows systems to exchange messages

(llusion of a single system

C ti ; i t C(i t S



$1

Computing ;nvironments – C(ient-Server

Client-Server Computing

Dumb terminals supplanted by smart PCs Many systems nowservers, responding to requests generatedbyclients

Compute-server systemprovides an interface to client torequest services (i.e., database)

File-server systemprovides interface for clients to storeand retrieve files

C ti ; i t < t <



$2

Computing ;nvironments - <eer-to-<eer

Another model of distributed system

&8& does not distinguish clients and servers

(nstead all nodes are considered peers

!ay each act as client' server or both

0ode must join &8& networ

6egisters its service with central looupservice on networ' or

roadcast re.uest for service and

respond to re.uests for service via

discovery protocol

Examples include 0apster and @nutella ,7oice over I< 47oI<5 such as /ype

C ti ; i t 7i t (i ti



$

Computing ;nvironments - 7irtua(i)ation

Allows operating systems to run applications within other O/es

9ast and growing industry

;mu(ation used when source #&" type different from target type

4i3e3 &ower&# to (ntel xC5

@enerally slowest method

*hen computer language not compiled to native code %Interpretation

7irtua(i)ation % O/ natively compiled for #&"' running guest O/es

also natively compiled

#onsider 9!ware running *inF& guests' each running

applications' all on native *inF& host O/

744 4virtual machine !anager5 provides virtualization

services

Comp ting ;n ironments 7irt a(i ation



$#


"se cases involve laptops and destops running multiple O/es for

exploration or compatibility

Apple laptop running !ac O/ F host' *indows as a guest

+eveloping apps for multiple O/es without having multiple

systems

GA testing applications without having multiple systems

Executing and managing compute environments within data

centers

9!! can run natively' in which case they are also the host

There is no general purpose host then 49!ware E/F and #itrix

Fen/erver5

Computing ;nvironments 7irtua(i)ation



$$


Computing ;nvironments C(oud Computing



$6

Computing ;nvironments – C(oud Computing

+elivers computing' storage' even apps as a service across a networ

7ogical extension of virtualization because it uses virtualization as the base for it

functionality3

Amazon ;C2 has thousands of servers' millions of virtual machines' petabytes

of storage available across the (nternet' pay based on usage

!any types

<ub(ic c(oud % available via (nternet to anyone willing to pay

<rivate c(oud % run by a company for the company,s own use

9ybrid c(oud % includes both public and private cloud components

/oftware as a /ervice 4SaaS5 % one or more applications available via the

(nternet 4i3e3' word processor5

&latform as a /ervice 4<aaS5 % software stac ready for application use via the

(nternet 4i3e3' a database server5 (nfrastructure as a /ervice 4IaaS5 % servers or storage available over (nternet

4i3e3' storage available for bacup use5




$,


#loud computing environments composed of traditional O/es' plus

9!!s' plus cloud management tools

(nternet connectivity re.uires security lie firewalls

7oad balancers spread traffic across multiple applications

Computing ;nvironments ea( 8ime ;mbedded Systems



$

Computing ;nvironments – ea(-8ime ;mbedded Systems

6eal-time embedded systems most prevalent form of computers

9ary considerable' special purpose' limited purpose O/' rea(-timeOS

"se expanding

!any other special computing environments as well

/ome have O/es' some perform tass without an O/

6eal-time O/ has well-defined fixed time constraints

&rocessing must be done within constraint

#orrect operation only if constraints met

Open-Source Operating Systems



$

Open-Source Operating Systems

Operating systems made available in source-code format rather than just

binary c(osed-source

#ounter to the copy protection and 'igita( ights 4anagement

.'4 movement

/tarted by %ree So&t*are %oundation .%S%' which has 1copyleft2

? <ub(ic =icense .<=

Examples include ?3=inu and >S' ?ID 4including core of 4ac

OS D5' and many more

#an use 9!! lie 9!ware &layer 4;ree on *indows5' 9irtualbox

4open source and free on many platforms - http:))www3virtualbox3com5

"se to run guest operating systems for exploration



;nd o& Chapter 1

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61

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