Chapter 14 Operating System

8/12/2019 Chapter 14 Operating System

1/54

Computer Fundamentals: Pradeep K. Sinha & Priti SinhaComputer Fundamentals: Pradeep K. Sinha & Priti Sinha

Slide 1/54Chapter 14: Operating SystemsRef Page

Chapter 14Operating Systems


2/54



Learning ObjectivesLearning Objectives

In this chapter you will learn about:

Definition and need for operating system

Main functions of an operating system

Commonly used mechanisms for:

Process management Memory management

File management

Security

Command interpretation module

Some commonly used OS capability enhancement software

Some popular operating systems

251


3/54



Integrated set of programs that controls the resources(the CPU, memory, I/O devices, etc.) of a computersystem

Provides its users with an interface or virtual machine

that is more convenient to use than the bare machine Two primary objectives of an OS are:

Making a computer system convenient to use

Managing the resources of a computer system

Definition and Need for OSDefinition and Need for OS

251


4/54



The operating systemlayer hides the details ofthe hardware from theprogrammer and

provides the programmerwith convenient interfacefor using the system

Users

Operating System

ComputerHardware

OtherSystem Software andApplication Programs

Logical Architecture of a Computer SystemLogical Architecture of a Computer System

252


5/54



Process management

Memory management

File management

Security

Command interpretation

Main Functions of an OSMain Functions of an OS

252


6/54



Throughput: Amount of work that the system is able todo per unit time

Turnaround time: Interval from the time of submissionof a job to the system for processing to the time ofcompletion of the job

Response time: Interval from the time of submission of ajob to the system for processing to the time the firstresponse for the job is produced by the system

Parameters for Measuring SystemPerformance

Parameters for Measuring SystemPerformance

253


7/54



A process (also calledjob) is a program in execution

Process management manages the processessubmitted to a system in a manner to minimize idle timeof processors (CPUs, I/O processors, etc.) of the system

Process ManagementProcess Management

253


8/54



Manual loading mechanism: Jobs were manuallyloaded one after another in a computer by thecomputer operator

Batch processing mechanism: Batch of jobs wassubmitted together to the computer and job-to-jobtransition was done automatically by the operatingsystem

Job Control Language (JCL): Control statementswere used to facilitate job loading and unloading

Process Management Mechanisms inEarly Systems

Process Management Mechanisms inEarly Systems

253


9/54



$JOB, ONGC05839,USER=SINHA

$COBOL

COBOL program

Data for program

$LOAD$RUN

$END

Use of Job Control Statements in BatchProcessing (An Example)

Use of Job Control Statements in BatchProcessing (An Example)

255


10/54



Uniprogramming: Only one job is processed at atime and all system resources are available exclusivelyfor the job until its completion

Multiprogramming: Interleaved execution of two ormore different and independent programs by a

computer Types of Multiprogramming:

Multiprogramming with fixed tasks (MFT): Fixednumber of jobs can be processed concurrently

Multiprogramming with variable tasks (MVT):

Number of jobs can vary

Area occupied by each job residing simultaneously inthe main memory is known as a memory partition

MultiprogrammingMultiprogramming

255


11/54



CPU bound: Mostly perform computations with littleI/O operations. Scientific and engineeringcomputations usually fall in this category

I/O bound: Mostly perform I/O operations with little

computation. Commercial data processing applicationsusually fall in this category

JobJob

255


12/54



Only one job is processed by the system at a time and allthe system resources are exclusively available for the jobuntil it completes

Main memory

User program area

OS area

Execution inprogress

CPU

Operatingsystem

User job

Uniprogramming SystemUniprogramming System

255


13/54



Secondary disk storage

Writing output data

Main memory

Execution inprogress

CPU

Operating system

Job C

(Waiting for CPU)

Job A

Job B

Multiprogramming SystemMultiprogramming System

257


14/54



Ready Running

Blocked

New

job

Job is allocated the

CPU for execution Job

processing

completed

I/O completed Job must wait for I/O

completion

Process States in MultiprogrammingProcess States in Multiprogramming

257


15/54



Large memory

Memory protection

Job status preservation

Proper job mix (CPU and I/O bound jobs)

CPU scheduling

Requirements of Multiprogramming SystemsRequirements of Multiprogramming Systems

257


16/54



process identifier

process state

program counter

values of various CPU

registers

accounting and schedulinginformation

I/O status information

PCB is used to preserve the job status of each loadedprocess in a multiprogramming system

Process Control Block (PCB)Process Control Block (PCB)

257


17/54



Interleaved execution of multiple jobs (often referredto as tasks of same user) in a single-user system

Computer systems used for multitasking areuniprocessor systems (having only one CPU)

Treated differently from multiprogramming that refersto interleaved execution of multiple jobs in a multi-user system

MultitaskingMultitasking

258


18/54



Thread is basic unit of CPU utilization. Threads

share a CPU in the same way as processes do

All threads of a process also share the same set of

operating system resources

All threads of a process inherit parents address

space and security parameters

Each thread of a process has its own program

counter, its own register states, and its own stack

Referred as mini-process or lightweight process

MultithreadingMultithreading

258


19/54



(a) Single-threaded and (b) multithreaded processes. Asingle-threaded process corresponds to a process of atraditional operating system. [Reproduced with

permission, from the book titled Distributed OperatingSystems: Concepts and Design by Pradeep K. Sinha. 1997 IEEE, USA].

Address space

ThreadAddress space

Thread Thread Thread

Multithreading SystemMultithreading System

259


20/54



System with two or more CPUs having ability to executemultiple processes concurrently

Multiple CPUs are used to process either instructions fromdifferent and independent programs or differentinstructions from the same program simultaneously

Types of multiprocessing:

Tightly-coupled: Single system-wide primary memoryshared by all processors

Loosely-coupled: Each processor has its own local

memory

MultiprocessingMultiprocessing

259


21/54



I/O Units I/OProcessors

CPU

Mainmemory

CPU, Memory, and I/O Processors of aComputer System

CPU, Memory, and I/O Processors of aComputer System

260


22/54



CPU-1Main

memoryCPU-2

I/Oprocessors

I/Oprocessors

I/O units I/O units

Multiprocessing SystemMultiprocessing System

260


23/54



Simultaneous interactive use of a computer system bymany users in such a way that each one feels thathe/she is the sole user of the system

User terminals connected to the same computersimultaneously

Uses multiprogramming with a special CPU schedulingalgorithm

Short period during which a user process gets to useCPU is known as time slice, time slot, or quantum

CPU is taken away from a running process when theallotted time slice expires

Time-sharingTime-sharing

261


24/54



Ready Running

Blocked

New

Job

Job is allocated to

CPU for executionJob

processing

completed

I/O completed Job must wait

for I/O

completion

Allotted time slice is over

Process State Diagram for a Time-SharingSystem

Process State Diagram for a Time-SharingSystem

261


25/54



Reduces CPU idle time

Provides advantages of quick response time

Offers good computing facility to small users

Advantages of Time-sharing SystemsAdvantages of Time-sharing Systems

262


26/54



Memory is important resource of a computer systemthat must be properly managed for the overall systemperformance

Memory management module:

Keeps track of parts of memory in use and parts notin use

Allocates memory to processes as needed anddeallocates when no longer needed

Memory ManagementMemory Management

262


27/54



Used in systems that process one job only at a time, andall system resources are available exclusively for the jobuntil it completes

Simple and easy to implement

Does not lead to proper utilization of the main memory asunoccupied memory space by the currently active userprocess remains unused

Used only on very small or dedicated computer systems

Uniprogramming Memory ModelUniprogramming Memory Model

262


28/54



Unused

Operating system

User process

Operating system area

User area

Uniprogramming Memory ModelUniprogramming Memory Model

263


29/54



Two memory management schemes used to facilitate thisare:

Multiprogramming with fixed number of memorypartitions: User area of the memory is divided into a

number of fixed-sized partitions Multiprogramming with variable number of memory

partitions: Number, size and location of the partitionsvary dynamically as processes come and go

Multiprogramming Memory ModelsMultiprogramming Memory Models

263


30/54



Operatingsystem

Partition 1

Partition 2

Partition 3

Partition n

Operating systemarea

User area dividedinto n equal-sized

partitions

Multiprogramming with Fixed Number of MemoryPartition

Multiprogramming with Fixed Number of MemoryPartition

263


31/54



Operatingsystem

Free

Operatingsystem

Free

P1

Operatingsystem

Free

P1

P2Userarea

Time

P1

comes

P2

comes

P3

comes

(a) (b) (c)

Operatingsystem

Free

P1

P2

P3

(d)The number, size, and location of the partitions varydynamically as processes come and go. (contd)

Multiprogramming with Variable Number ofMemory Partitions

Multiprogramming with Variable Number ofMemory Partitions

264


32/54


33/54


34/54



Three basic concepts used for its realization are:

On-line secondary storage: Used to keep a processsaddress space ready to be loaded into the memory

Swapping: Process of transferring a block of data fromthe on-line secondary storage to main memory

(swapping in) or vice-versa (swapping out)

Demand paging: Scheme of swapping in of pages of aprocess as and when needed during execution of theprocess, rather than loading all the pages beforestarting the processs execution

Virtual Memory RealizationVirtual Memory Realization

265


35/54



Provides a large virtual memory to programmers on asystem having smaller physical memory

Enables execution of a process on a system whose mainmemory size is less than the total memory required by theprocess

Enables a processs execution to be started even whensufficient free memory for loading the entire process is notavailable

Makes programming easier there no longer need to worryabout the memory size limitations

Often leads to less I/O activity resulting in betterthroughput, turnaround time, and response time

Advantages of Virtual MemoryAdvantages of Virtual Memory

266


36/54


37/54



A file is a collection of related information

Every file has a name, its data and attributes

Files name uniquely identifies it in the system and is usedby its users to access it

Files data is its contents

Files attributes contain information such as date & time ofits creation, date & time of last access, date & time of lastupdate, its current size, its protection features, etc.

File management module of an operating system takes

care of file-related activities such as structuring,accessing, naming, sharing, and protection of files

File ManagementFile Management

266


38/54



Two commonly supported file access methods are:

Sequential access: Information stored in a file can beaccessed sequentially (in the order in which they arestored, starting at the beginning)

Random access: Information stored in a file can beaccessed randomly irrespective of the order in whichthe bytes or records are stored

File Access MethodsFile Access Methods

267


39/54



Set of commands provided by an operating system todeal with files and their contents

Typical file operations include create, delete, open,close, read, write, seek, get attributes, set attributes,rename, and copy

File OperationsFile Operations

267


40/54



File naming deals with the rules for naming files in anoperating system. This may include such rules as:

Maximum number of characters that a file name mayhave

Special characters allowed in a file name

Distinction between upper case and lower case letters

Multi-part file names allow file extensions to be part of afile name. File extensions indicate something about thefile and its content

Used by applications to check for the intended type offile before operating on it

File NamingFile Naming

268


41/54


42/54



Its meaning

Online manual page file

General text file

Backup file

Microsoft word document file

Microsoft windows sound file

Lotus 1-2-3 spreadsheet file

Microsoft Excel spreadsheet file

JPEG graphics file

File extension

.man

.txt

.bak

.doc

.wav

.wk4

.xls

.jpg

.gif GIF graphics file

(Continued from previous slide)

File Extensions (Example)File Extensions (Example)

268


43/54



Deals with protecting the various resources and informationof a computer system against destruction and unauthorizedaccess

External security: Deals with securing computer againstexternal factors such as fires, floods, earthquakes, stolen

disks/tapes, etc. by maintaining adequate backup, usingsecurity guards, allowing access to sensitive information toonly trusted employees/users, etc.

Internal security: Deals with user authentication, accesscontrol, and cryptography mechanisms

SecuritySecurity

269


44/54



User authentication: Deals with the problem ofverifying the identity of a user (person or program)before permitting access to the requested resource

Access Control: Once authenticated, access controlmechanisms prohibit a user/process from accessing those

resources/information that he/she/it is not authorized toaccess

Cryptography: Means of encrypting private informationso that unauthorized access cannot use information

SecuritySecurity

269


45/54



Provides a set of commands using which the user can giveinstructions to the computer for getting some job done byit

Commands supported by the command interpretationmodule are known as system calls

(Continued on next slide)

Command InterpretationCommand Interpretation

269


46/54



Two types of user interfaces supported by various operatingsystems are:

Command-line interface: User gives instructions tothe computer by typing the commands

Graphical User Interface (GUI): User givescommands to the system by selecting icon or menuitem displayed on the screen with the use of a point-and-draw device


Command InterpretationCommand Interpretation

269


47/54



Perform several tasks of routine nature, frequentlyneeded by users but are not provided as part of the OS

They are primarily grouped into three categories:

Translating programs: Translate a source program

into an object program

Library programs: Consist of frequently usedfunctions and operations

Utility programs: Assist users with systemmaintenance tasks such as disk formatting, data

compression, data backups, antivirus utilities

OS Capability Enhancement SoftwareOS Capability Enhancement Software

270


48/54



Developed in the early 1970s at Bell Laboratories by KenThompson and Dennis Ritchie

Written in C high-level language, hence, highly portable

Multi-user, time-sharing OS

Used on a wide variety of computers ranging fromnotebook computers to super computers

Especially prevalent on RISC workstations such as thosefrom Sun Microsystems, Hewlett-Packard, IBM, andSilicon Graphics

Structured in three layers kernel, shell, and utilities

UNIX OSUNIX OS

272


49/54



Stands for Microsoft Disk Operating System.

Single-user OS for IBM and IBM-compatible personalcomputers (PC)

Structured in three layers BIOS (Basic Input OutputSystem), kernel, and shell

Very popular in the 1980s, now not in much use anddevelopment with the launch of Microsoft Windows OS in1990s

MS-DOSMS-DOS

272


50/54



Developed by Microsoft to overcome limitations of MS-DOS operating system

Single-user, multitasking OS

Native interface is a GUI

Designed to be not just an OS but also a completeoperating environment

OS of choice for most PCs after 1990

Microsoft WindowsMicrosoft Windows

272


51/54



Multi-user, time-sharing OS developed by Microsoft

Designed to have UNIX-like features so that it can beused for powerful workstations, network, and databaseservers

Supports multiprogramming and is designed to takeadvantage of multiprocessing on systems havingmultiple processors

Native interface is a GUI

Built-in networking and communications features

Provides strict system security

Rich set of tools for software development

Microsoft Windows NTMicrosoft Windows NT

273

d l d h h


52/54



Open-source OS enhanced and backed by thousands ofprogrammers world-wide

Multi-tasking, multiprocessing OS, originally designed tobe used in PCs

Name Linux is derived from its inventor Linus Torvalds

Several Linux distributions available (Red Hat, SuSE).Difference in distribution is mostly set of tools, numberand quality of applications, documentation, support, andservice

LinuxLinux

273


53/54

C t F d t l P d K Si h & P iti Si hC t F d t l P d K Si h & P iti Si h


54/54




Throughput Tightly coupled system Time-sharing Time slice Time slot Translating programs

Turnaround time Unix User authentication Utility programs Virtual machine Virtual memory

Keywords/PhrasesKeywords/Phrases

274

Documents

Chapter 14 Operating System