OS-01

UNIT–I: Introduction• Introduction to Operating System Concepts

• Multitasking• Multiprogramming• Multiuser• Multithreading

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• Types of Operating Systems• Batch Operating System• Time–sharing Systems• Distributed OS• Network OS• Real–Time OS

• Various Operating System Services

• Architecture

• System Calls and Programs

• Exam Questions1Unit-I: Introduction

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Introduction to Operating System Concepts

• Prerequisites

• Operating System (OS)

• Resources of a Computer System

• User View

• System View

• Objectives and Functions of OS

• Multiprogramming

• Multitasking

• Multiuser

• Multithreading

2Unit-I: Introduction

• Basic Data Structures

• Computer Organisation

• High–Level Language (C, …)

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Unit-I: Introduction

Prerequisites

• Collection of System Software (Programs), which makes it User friendly andMost efficient

• Controls and coordinates use of Hardware among Various Applications and Users

KernelProgram running at all times on the Computer


Operating System

What is an Operating System?

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

• Operating system goals:– Execute user programs and make solving user problems easier– Make the computer system convenient to use– Use the computer hardware in an efficient manner


Computer System Structure

• Computer system can be divided into four components:– Hardware – provides basic computing resources

• CPU, memory, I/O devices– System Programs Operating System

• Controls 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• Word processors, compilers, web browsers, database systems,

video games– Users

• People, machines, other computers


• AT & T / BSDUnix

• Sun Microsystems’ Solaris 2 Linux• Microsoft MS-DOS Windows 95 / 98 / NT Windows 2000 (Windows Me) Windows XP Windows Vista

Windows 7 / Windows 8• DEC VMS (Virtual Memory System) TOPS–20 (Total Operations Processing System)• IBM OS/2

• AppleMacintosh


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Most Popular Operating Systems

Hardware and Software required to solve a problem

CPU Time

Memory Space

File Storage Space

I/O Devices

…


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Resources of a Computer System

Architecture : Four Components of a Computer System


• Goal• To maximize the work, the user performing

• Ease of use

• Don’t care about Resource utilization

• Shared computer Mainframe / Minicomputer• Share Resources• Exchange Information• Designed to maximize Resource utilization• All Available CPU Time, Memory and I/O used efficiently


User View

• Workstations• Connected to Networks of other workstations and Servers• Dedicated Resources at disposal• Also Share Resources such as Networking and Servers

• Handheld Computers• Standalone units for Individual users• Connected to Networks

(Directly by wire / through wireless Modems and Networking)

• Perform relatively few remote operations (Power, Speed, Interface limitations)

• Designed mostly for individual usability

• Embedded Computers in Home Devices and Automobiles• Have Numeric Keypads• May turn indicator lights on or off to show status• Designed primarily to run without user intervention


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User View

Most intimately involved with Hardware

• Resource Allocator• Acts as Manager of Resources.

• Decides to allocate Resources to Specific Programs and Users so that OS operates the Computer System Efficiently and Fairly

• Important when many Users access the same computer

• Control Program• Controls Execution of User Programs to prevent Errors and Improper use of

Computer

• Concerned with Operation and Control of I/O Devices


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System View

Operating System Definition

• OS is a resource allocator– Manages all resources– Decides between conflicting requests for efficient and fair resource use

• OS is a control program– Controls execution of programs to prevent errors and improper use of

the computer


Operating System Definition (Cont.)

• No universally accepted definition

• “The one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program.


Overview

• Multiprogramming: Running multiple programs “at the same time”– Requires multiplexing (sharing) the CPU

• Transfer of control is called a context switch


Computer System Organization• Computer-system operation

– One or more CPUs, device controllers connect through common bus providing access to shared memory

– Concurrent execution of CPUs and devices competing for memory cycles


Storage-Device Hierarchy


• Essential part of a Computer System

• Provides an Environment within which Other programs can do Useful work

• Program running at all times on the Computer (Kernel)

• Program that Manages Computer Hardware

• Program that acts as an intermediary between the User of a Computer and the Computer Hardware

• PurposeTo provide an environment in which a User can Execute Programs

in a Convenient and Efficient manner


Objectives and Functions of Operating System

• Must Ensure Correct Operation of Computer System

• Provides Certain Services to Programs and to the users of those programs in order to make their Tasks Easier

• Controls and Coordinates the use of Hardware among Various Application Programs for the Various users

• Primary GoalsUser friendlyEfficient Operation of the Computer System


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Objectives and Functions of Operating System

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Evolution of Operating Systems

• Serial Processing– No operating system– Machines run from a console with display lights,

toggle switches, input device, and printer– Schedule time– Setup included loading the compiler, source

program, saving compiled program, and loading and linking


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• Simple Batch Systems– Monitors• Software that controls the sequence of events• Batch jobs together• Program branches back to monitor when finished


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Hardware Features

• Memory protection– Do not allow the memory area containing the

monitor to be altered

• Timer– Prevents a job from monopolizing the system


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Hardware Features

• Privileged instructions– Certain machine level instructions can only be

executed by the monitor

• Interrupts– Early computer models did not have this capability


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Memory Protection

• User program executes in user mode– Certain instructions may not be executed

• Monitor executes in system mode– Kernel mode– Privileged instructions are executed– Protected areas of memory may be accessed


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Major Achievements

• Processes• Memory Management• Information protection and security• Scheduling and resource management• System structure


• Single User System

• Single Program in execution.


Uniprogramming

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Uniprogramming

• Processor must wait for I/O instruction to complete before preceding


No. of Programs in execution.

Increases CPU utilisation by organizing jobs so thatthe CPU always has one job to execute.

CPU is never idle.

OS Keeps several jobs in memory simultaneously.Picks and begins to execute one of the jobs in the memory.

Job may have to wait for some task (I/O operation) and OS simply switches to, and executes, another job.

When that job needs to wait, the CPU is switched to another job, and so on.

When the first job finishes waiting, it gets the CPU back.

Allow time-sharing.


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Multiprogramming

• Multiple Tasks are performed during the Same period of time.

• Tasks Share Common Processing Resourcessuch as CPU and Main Memory.

• In Uniprocessor Systems, Multitasking Solves the problem by Scheduling which task may be the one running at any given time, and when another waiting task gets a turn.

Context Switch • Act of reassigning a CPU from one task to another one.


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Multitasking / Multiprocessing

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Multiprogramming

• When one job needs to wait for I/O, the processor can switch to the other job


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Multiprogramming


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Time Sharing

• Using multiprogramming to handle multiple interactive jobs

• Processor’s time is shared among multiple users

• Multiple users simultaneously access the system through terminals


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Compatible Time-Sharing System (CTSS)

• First time-sharing system developed at MIT


Allows for Multiple users to use the Same Computer at the Same time and Different times.


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Multiuser

• Operating Systems that allow Different parts of a Software program to run Concurrently.

• Examples• Linux• Unix• Windows 2000

• Applications• Any kind of application which has Distinct tasks which can

be performed independently.

• Any application with a GUI.

• Any application which requires Asynchronous response.

• Network based applications are ideally suited.


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Multithreading

• Batch Processing Systems

• Interactive Systems

• Time Sharing

• Time Slicing

• Distributed Systems

• Network Systems

• Real–Time Systems


Types of Operating Systems|<<

Computer runs one and only one application at a time.

Early Computers were physically enormous machines run from a console.

Common input devices Card readersTape drives

Common output devicesLine printersTape drivesCard punches


Batch Processing Systems

OS always resident in memory.

CPU is often idle.

User did not interact directly with computer systems.

User prepared a job and submitted to computer operator.

Operators batched together jobs with similar needs and run them through the computer as a group.

Programmers would leave their programs with the operator.

The operator would sort the programs into batches with similar requirements and as the computer became available would run each job.


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Batch Processing

• User and Computer System interact.

• User Requests.

• System Responds.

• The process goes on.


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Interactive Processing

Variable CPU Time to different processes.

Once CPU Time is allocated to a process, will not be interrupted till it completes its execution, or waiting for an I/O,

or cannot continue its execution.


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Time Sharing

Equal Amount of CPU time allocated among Various Processes.


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Time Slicing

• Distribute the Computation among Several Physical Processors

• Loosely Coupled System• Each Processor has its Own Local Memory

• Processors Communicate with one another thru Various Communications lines, such as High–Speed buses.

• Enables Parallelism but speed up is not the goal


Distributed Systems

• Advantages of Distributed Systems• Resources Sharing• Computation Speed up–load Sharing

• Reliability• Communications

• Distributed Operating System• Less Autonomy between Computers• Gives the impression, Single Operating System Controlling the Network

• Types of Distributed Systems• Client–Server Systems• Peer–to–Peer Systems


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Distributed Systems

• Equal Amount of CPU time allocated among Various Processes.

• Autonomy between computers• File sharing, exchange of information between computers


Network Systems|<<

• Special purpose OS.•

• Used when rigid time requirements have been placed on the operation of a processor or the flow of data.

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• Used as control device in a dedicated application. Accurate response time.

• Sensors bring data to the computer. • The computer analyses the data and possibly adjust controls to modify

the sensor inputs.

• Well-defined, Fixed-time constraints.

• Processing must be done within the defined constraints.

Ex: Systems controlling scientific experimentsMedical imaging systemsIndustrial control systemsCertain display systemsAutomobile-engine fuel-injection systemsHome-appliance controllersWeapon systems


Real–Time Systems

Hard real-time systemsGuarantee critical tasks be completed on time.

Soft real-time systemsCritical real-time task gets priority over other tasks

and retains the priority until it completes.

Ex: Multimedia Advanced scientific projects Undersea exploration Planetary rovers


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Types of Real–Time Systems



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|<<Various Operating System Services

Provides No. of Services.

Lowest level – System CallsAllow running program to make requests

from the OS directly.

Higher level – Command Interpreter or ShellUser issues request without writing program.

CategoriesProgram ControlStatus RequestsI/O Requests


Operating System Services

– User Interface

– Program Execution

– I/O Operations

– File-System Manipulation

– Communications

– Error Detection

– Other Services

• Resource Allocation

• Accounting

• Protection and Security


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• All Operating Systems have User Interface (UI)

• Command-Line Interface (CLI)

• Graphics User Interface (GUI)


|<<User Interface

• Load Program into Memory

• Run the Program

• End Execution, either Normally or Abnormally (indicating Error)


Program Execution|<<

Running Program may require I/O,

which may involve File or I/O Device.


I/O Operations|<<

Programs need to

Read and Write Files and Directories,

Create and Delete Files and Directories,

Search Files and Directories,

List File Information,

Permission Management.


File–System Manipulation|<<

Processes may exchange information, on the Same Computer or between Computers over a Network

Communications may be via – Shared Memory or – thru Message Passing (Packets moved by the Operating System)


Communications|<<

• May occur in – the CPU and Memory Hardware, – I / O Devices, – User Program

• For each type of Error, – OS should take the appropriate action

to ensure correct and consistent computing

• Debugging facilities – can greatly enhance the User’s and Programmer’s abilities

to efficiently use the System


Error Detection|<<

When Multiple Users or Multiple Jobs running Concurrently,

Resources must be Allocated to each of them.


Resource Allocation|<<

To Keep Track of

Which Users use How much

What Kinds of Computer Resources


Accounting|<<

• Protection – Involves ensuring that all Access to System Resources is Controlled

• Security of the System – from outsiders requires User Authentication, – extends to defending External I / O Devices from Invalid Access

attempts


Protection and Security|<<

• Hardware

• Operating System

• Application Programs

• Users


Basic Structure/Components of a Computer System

Central Processing Unit (CPU)

Memory

Input–Output (I/O) / Peripheral Devices

•Provides basic Computing Resources.


Hardware

Word Processors (MS–Word)

Spreadsheets (MS–Excel)

Compilers (C, Java, …)

Web Browsers (Internet Explorer, Mozilla)

Database Systems

Video Games

Define the ways in which the resources are used to solve the computing problems of the users.


Application Programs

• People

• Machines

• Other Computers


|<<Users

|<<System Calls and Programs


• System Calls• Types of System Calls

• System Programs


System Calls

System call is a Programming interface to the services provided by the OS

It provides Interface between Running Program and the Operating System.

Generally available as Assembly–Language Instructions.

• Typically written in a high-level language (C or C++)

• Mostly accessed by programs via a high-level Application Program Interface (API)rather than direct system call use.

• Methods used to Pass Parameters between a Running Program and the Operating System.

– Pass Parameters in Registers.– Store the Parameters in a Table in Memory, and the Table Address is passed as a

Parameter in a Register.– Push (store) the Parameters onto the Stack by the Program, and Pop off the Stack by

Operating System.

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API - System Call- OS relationship

Unit-I: Introduction 65

Typically a number is associated with each system call.System call interface maintains a table indexed according to

these numbersThe System call interface invokes the intended system call in OS

kernel and returns the status of the system call and any return values.

• The caller need know nothing about how the system call is implemented

• Just needs to obey API and understand what OS will do as a result call

• Most details of OS interface hidden from programmer by API



Types of System Calls

• Process Control

• File Management

• Device Management

• Information Maintenance

• Communications

• Example

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• End, Abort

• Load, Execute

• Create Process, Terminate Process

• Get Process Attributes, Set Process Attributes

• Wait for time

• Wait Event, Signal Event

• Allocate and Free Memory


|<<System Calls – Process Control

• Create File, Delete File

• Open, Close

• Read, Write, Reposition

• Get File attributes, Set File attributes


|<<System Calls – File Management

• Request Device, Release Device

• Read, Write, Reposition

• Get Device attributes, Set Device attributes

• Logically Attach or Detach Devices


|<<System Calls – Device Management


• Get Time or Date, Set Time or Date

• Get System Data, Set System Data

• Get Process, File, or Device attributes

• Set Process, File, or Device attributes

|<<System Calls – Information Maintenance


• Create, Delete Communication connection

• Send, Receive Messages

• Transfer Status information

• Attach or Detach Remote Devices

|<<System Calls – Communications

System Call Sequence to Copy the contents of One file to another file.


|<<Example of System Calls


Provide Convenient environment for Program Development and execution.

Categories

•File Management

•Status information

•File Modification

•Programming Language Support

•Program Loading and Execution

•Communications

|<<System Programs


Create

Delete

Copy

Rename

Print

Dump

List

Manipulate Files and Directories

|<<System Programs – File Management


Date

Time

Amount of available Memory / Disk Space

No. of users

…

|<<System Programs – Status information


Text Editors

To Create and Modify the Contents of Files Stored on Disk or Tape.

Screen Editor – vi

Line Editor – edlin, ed, …

|<<System Programs – File modification


• Compilers

• Assemblers

• Interpreters

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System Programs – Programming Language Support


• Absolute Loaders

• Relocatable Loaders

• Linkage Editors

• Overlay Loaders

• Debugging Systems

|<<System Programs – Program Loading & Execution


Provide mechanism for creating virtual connections among processes, users and different computer

systems.

Allow users to Send messages to one another’s Screens.Browse Web pages.Send Electronic Mail messages.Log-in Remotely.Transfer Files from one machine to another.

|<<System Programs – Communications

Exam Questions1. Define OS.

2. Write about Evolution of Operating Systems.

3. Explain basic Structure of a Computer System & also Explain its basic elements.

4. Discuss the basic components of a virtual computer.

5. What are OS Objectives?

6. What is an Operating System? Explain the functions of OS.

7. Discuss the various approaches of designing an operating system.

8. Write about Multitasking.

9. Explain the concept of Multiprogramming. 81Unit-I: Introduction

Exam Questions

10. What are the multi-tasking, multi-programming and multi-threading?

11. Explain the following:a. Multiprogrammingb. Timesharingc. Virtual Memory

12. What are Distributed Operating Systems?

13. What are the types of real-time systems?

14. What is dispatcher?

15. What is a system call? Explain the categories of system calls.

16. What is a system call? Explain different types of system calls.

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Documents

OS-01