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Operating Systems (IIOS-332C)

Introduction to Operating

Systems

• All desktop computers use an operatingsystem.

• Common desktop operating systems include:– Windows

– Unix

– Linux

• There are hundreds of other operatingsystems available for special-purposeapplications e.g. mobile phones, PDAs etc.

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.

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

Resources of Computer System

Computer System

Processor

Memory and

Disks

Files

Input Output Devices

5

Computer System Structure

Computer System

Software

System Software

Application Software

Hardware

Language

Translators

Operating

system

Four Components of a Computer

System

8

Components of an Operating

System

Operating system – part of the computing system

that manages all of the hardware and all of the

software

– Controls every file, device, section of main memory &

every nanosecond of processing time

• Memory manager

• Processor manager

• Device manager

• File manager

Operating system

consists of

9

Coordination of Operating System

10

Types of Operating Systems

• GUI

• Examples

– Windows: Everything is presented to user graphically

– Mac OSX

– Linux running xWindows

• CUI

• Examples

– MS-DOS

– Unix

Types of Operating Systems

• Single user OS

– MS-DOS

– Windows 1.0

– Windows 2.x , Windows 3.x , Windows 95

Windows 98, Windows ME

• Multi user OS

– Unix, Windows NT, 2000, XP

11

Types of Operating Systems

• Single User

– Serial Processing OS

• Working in serial manner: Card Reader

– Batch Processing OS

• Batch of jobs can be executed together.

12

13

Types 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

14

Types of Operating Systems

• Simple Batch Systems• Software that controls the sequence of events

• Batch jobs together

• Example: The concept of batch files in DOS and Unix.

Types of Operating Systems

• Types of Multi User OS

– Multiprogramming OS

– Time Sharing OS

– Multiprocessing OS

15

Why Multiprogramming

• To have maximum utilization of

the CPU

16

17

The CPU is wasted if a job waits for I/O. This leads to:

– Multiprogramming (dynamic switching ). Whileone job waits for a resource, the CPU can findanother job to run. It means that several jobsare ready to run and only need the CPU in orderto continue.

All of this leads to:

– memory management

– resource scheduling

– deadlock protection

Why Multiprogramming

Why Time Sharing

• Time Sharing - multiprogramming

environment that's also interactive.

• Fair Scheduling is also important……

18

Working of Processor

• In Uniprogramming Way….

• In Multiprogramming Way…..

19

20

Uniprogramming

• Processor must wait for I/O instruction to

complete before preceding

21

Multiprogramming

• When one job needs to wait for I/O, the

processor can switch to the other job

22

Multiprogramming

23

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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• Multiprocessing- Specific applications….

• Multiple Processor may be there…..

• System can communicate via shared memory…..

• Speed improvement by putting together anumber of processors.

.

Why Multiprocessing

Types of Operating Systems

• Multi User OS

– Distributed Operating System

– Network Operating System

25

Distributed Operating System

A distributed system is a collection of

autonomous computers that appear to

the users of the system as a single

computer.

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• Distributed Systems - communicate viamessage passing.

• Advantages include resource sharing, speedup, reliability, communication.

• There is a single system image

Why Distributed OS

• By contrast, one could imagine an operating

system in which users are never concerned with

where their programs run, or the location of any

resources.

• The operating system has control over all the

nodes in the system, and it transparently locates

new processes at whatever node suits its

scheduling policies.

Distributed Operating System

Why Distributed Systems?

• Resource sharing

• Scalability

• Reliability

• Need for higher processing speed

• Spatial distribution is inherent in many applications

Network Operating System

• It provides an environment where users are

aware of the multiplicity of machines.

• Users can access remote resources by

– logging into the remote machine OR

– transferring data from the remote machine to

their own machine

• Users should know where the required files

and directories are….

• Each machine could act like a server and a

client at the same time.

Types of Operating Systems

• Special Operating System

– Real Time Operating System

• Hard Real Time

• Soft Real Time

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What are Real-time Systems ?

Those systems in which the correctness of the

system depends not only on the logical result of

computation, but also on the time at which the

results are produced.

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Types of Real Time Systems

• Based on Hard deadline: Penalty due to missing

deadline is a higher order of magnitude than the

Reward in meeting the deadline.

• Based on Soft deadline: Penalty often equal /

lesser magnitude than Reward.

Soft RTOS…

• In a soft real-time system, it is considered undesirable, but not catastrophic, if deadlines are occasionally missed.

• Also known as “best effort” systems

• Most modern operating systems can serve as the base for a soft real time systems.

• Examples:

– multimedia transmission and reception,

– networking, telecom (cellular) networks,

– web sites and services

– computer games.

Hard RTOS…

• A hard real-time system has time-critical deadlines that must be met; otherwise a catastrophic system failure can occur.

• Absolutely, positively, first time every time

• Requires formal verification/guarantees of being to always meet its hard deadlines (except for fatal errors).

• Examples:

– air traffic control

– vehicle subsystems control

– Nuclear power plant control

Types of Operating Systems

• Special Operating System

– Embedded Operating System

– Parallel Operating System

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What is an Embedded OS?

• An "embedded system" is any computer system or

computing device that performs a dedicated function

or is designed for use with a specific embedded

software application.

• Embedded systems may use a ROM-based

operating system or they may use a disk-based

system, like a PC. But an embedded system is not

usable as a commercially viable substitute for

general purpose computers or devices.

Example of Parallel Processing

Environment

MPP Massively Parallel ProcessorSMP Symmetric Multi-Processor

cpu cpu cpu

Fast Interconnect

Memory (shared)

cpu

Mem

cpu

Mem

cpu

Mem

Interconnect (varies)

P PP P P P..

Microkernel

Multi-Processor Computing System

Threads Interface

Hardware

Operating System

ProcessProcessor ThreadP

Applications

Parallel Computing

Environment

Programming paradigms

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Brief History of Operating

Systems Development

1940 1955 1965 1980

1990

First Generation

Vacuum tube, single

user, early operating

systems

Second Generation

Job scheduling, JCL,

faster I/O, spooling,

batch, files

Third Generation

Shared processing,

multiprogramming, virtual

memory, DBMS

Recent Developments

Distributed computing,

personal computers, high-

speed communication, multi-

media

Syllabus

• Operating System Structures

– General OS task: resource mgmt, Sharing & Protection

– OS Interfaces: shells, API, system calls

– Architecture of OS

– Layered system design

– Microkernels

– Modularized approach

– Virtual Machines

– System Boot process

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Syllabus

• Process Concept

• Overview

• Scheduling

• Operations

• Interprocess Communication

• Process Vs. Thread

• Multithreaded Programming

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Syllabus

• Process Scheduling

– Scheduling Criteria

– Scheduling Algorithm

– Multi-Processor Scheduling

– Algorithm Evaluation

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Syllabus

• Process Synchronization

– Mutual exclusion

– Critical sections

– Classical synchronization problems

– Bounded Buffers

– Readers/writers

– Dining Philosophers

– Atomic transactions (cf. databases)

– Logging, UNDO/REDO recovery

– Concurrency Control, Serializability, Locking Time-

Stamping 44

Syllabus

Deadlocks

• Define the problem, give necessary conditions!– Graph-based models (single vs. multiple resources per type)

– Resource Allocation Graph

– Wait-For Graph

• Deadlock Prevention and Detection

• How/when can we detect that the system/some

processes is/are in a deadlock state?

• Recovery from deadlock

• If we detected a deadlock: how to resolve the

situation? 45

Syllabus

• Memory Management

– Background

– Swapping

– Memory Allocation Techniques

– Paging

– Segmentation

46

Syllabus

• Virtual- Memory Management

– Background

– Demand Paging

– Copy-on-Write

– Page Replacement

– Allocation of Frames

– Thrashing

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Syllabus

• File Management

– File Concept

– Access Methods

– Directory Structure

– File System Mounting

– File Sharing

– Protection

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Syllabus

• Implementing File System

– File System Structure

– File System Implementation

– Directory Implementation

– Allocation Methods

– Free Space Management

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Syllabus

• Mass Storage Structure

– Physical characteristics & performance

determinants of disk technology

– Connecting disks and processors

– Disk scheduling

– Different algorithms with their pros & cons

– Overcoming disk failures

– Storage hierarchy, tertiary storage

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Syllabus

• I/O Systems

– Transforming application-level commands into device

operations

– Analyze the steps necessary & point out major OS

tasks

– Ports, polling, interrupts, DMA, device drivers, kernel

I/O

– Show how interrupt handling is done in the OS!

– Why several levels (priorities), masking, etc.?

– Blocking vs. non-blocking vs. asynchronous I/O

– Give an example, show principal steps of interaction

between user process and OS components 51

Syllabus

• Protection

– Goals, principles, mechanisms of protection

– Model used for protection (objects, domains, access-

rights)

– Access matrix

– Addition of rights

– Revocation of rights

– Capabilities vs. access control lists

– Roles

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Points to note…………

• Major areas

– Processor Management

– Memory Management

– File Management

– Disk Management

– Input/ Output Management

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Functions of an OS

• Processor management

• Memory management

• Device management

• Storage management

• Application interface

• User interface

Processor Management

• The OS has tomanage theexecution ofprocesses so thatyou believe thatthere are severalthings happeningat once.

Processor Management

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However, the processor can only do onething at a time.

In order to give the appearance of lots ofthings happening at the same time, the OShas to switch between different processesthousands of times a second making surethat each process and application receivesenough of the processor's time to functionproperly.

Memory Management

• The OS manages memory (RAM). Whenapplications are loaded they need memory to workwith. The OS allocates software RAM to work in. Itensures that the RAM allocated is not used byanother application.

• The OS also manages virtual memory. In thisway the computer can run more applications thanit has RAM for. For example if a computer wasrunning a word processor and the user wanted toload a spreadsheet application at the same timeand there was not enough RAM then the OS usesthe hard disc as virtual RAM.

Device Management (Input/Output)

• The OS makes use of queues and buffers, specialstorage facilities that take a stream of bits (data)from a device, e.g. a keyboard, hold those bits, andthen release them to the CPU at a rate slow enoughfor the CPU to cope with.

• This function is very important when a number ofprocesses are running and taking up processortime. The OS will instruct a buffer to continue takinginput from the device, but to stop sending data tothe CPU while the process using the input issuspended. Then, when the process needing inputis made active once again, the OS will commandthe buffer to send data.

Device Management (Drivers)

• The operating system needs to communicate withthe various hardware components which make upthe computer. Special programs called driversenable the OS to communicate with these hardwaredevices. Drivers are needed as the hardware whichmakes up a PC may be vastly different to that ofanother PC with the same OS installed.

• Drivers are translation programs which convert themessages from the OS into messages that thehardware device can understand.

User Interface

• The user interface (UI) brings structure to the interaction between a user and the computer.

GUI

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Operating Systems in Practice

MS-DOS Operating System

Windows Operating System

UNIX/Linux Operating System

IBM OS/390 Operating System

Open Source Operating System

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Operating System Objectives

• Convenience

– Makes the computer more convenient to use

• Efficiency

– Allows computer system resources to be used in an

efficient manner

• Ability to evolve

– Permit effective development, testing, and introduction

of new system functions without interfering with service

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Services Provided by the

Operating System

• Program development

– Editors and debuggers

• Program execution

• Access to I/O devices

• Controlled access to files

• System access

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Services Provided by the

Operating System

• Error detection and response

– Internal and external hardware errors

• Memory error

• Device failure

– Software errors

• Arithmetic overflow

• Access forbidden memory locations

– Operating system cannot grant request of application

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Services Provided by the

Operating System

• System Accounting

– Collect usage statistics

– Monitor performance

– Used to anticipate future enhancements

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Kernel

• Portion of operating system that is in main

memory

• Contains most frequently used functions

• Also called the nucleus

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Job Control Language (JCL)

• Special type of programming language

• Provides instruction to the monitor an executing

unit

– What compiler to use

– What data to use

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Processes

• A program in execution

• An instance of a program running on a computer

• The entity that can be assigned to and executedon a processor

• A unit of activity characterized by a singlesequential thread of execution, a current state,and an associated set of system resources

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Difficulties with Designing

System Software

• Improper synchronization

– Ensure a process waiting for an I/O device receives the

signal

• Failed mutual exclusion

• Nondeterminate program operation

– Program should only depend on input to it, not on the

activities of other programs

• Deadlocks

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Process

• Consists of three components

– An executable program

– Associated data needed by the program

– Execution context of the program

• All information the operating system needs to manage the

process

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Memory Management

• Process isolation

• Automatic allocation and management

• Support of modular programming

• Protection and access control

• Long-term storage

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Virtual Memory

• Allows programmers to address memory from a

logical point of view

• No gap between the execution of successive

processes while one process was written out to

secondary store and the successor process was

read in

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Virtual Memory and File

System

• Implements long-term store

• Information stored in named objects called files

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Information Protection and

Security

• Availability

– Concerned with protecting the system against

interruption

• Confidentiality

– Assuring that users cannot read data for which access

is unauthorized

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Information Protection and

Security

• Data integrity

– Protection of data from unauthorized modification

• Authenticity

– Concerned with the proper verification of the identity of

users and the validity of messages or data

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Scheduling and Resource

Management

• Fairness

– Give equal and fair access to resources

• Differential responsiveness

– Discriminate among different classes of jobs

• Efficiency

– Maximize throughput, minimize response

time, and accommodate as many uses as

possible

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System Structure

• View the system as a series of levels

• Each level performs a related subset of functions

• Each level relies on the next lower level to perform

more primitive functions

• This decomposes a problem into a number of

more manageable subproblems

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Modern Operating Systems

• Multithreading

– Process is divided into threads that can run

concurrently

• Thread

– Dispatchable unit of work

– executes sequentially and is interruptable

• Process is a collection of one or more threads

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Modern Operating Systems

• Symmetric multiprocessing (SMP)

– There are multiple processors

– These processors share same main memory and I/O

facilities

– All processors can perform the same functions

Characteristics of Modern

Operating Systems

• Microkernel architecture

– assigns only a few essential functions to the kernel

• address space

• interprocess communication (IPC)

• basic scheduling

Characteristics of Modern

Operating Systems

• Multithreading

– process is divided into threads that can run

simultaneously

• Thread

– dispatchable unit of work

– executes sequentially and is interruptable

• Process is a collection of one or more threads

Characteristics of Modern

Operating Systems

• Symmetric multiprocessing

– there are multiple processors

– these processors share same main memory and I/O

facilities

– All processors can perform the same functions

Characteristics of Modern

Operating Systems

• Distributed operating systems

– provides the illusion of a single main memory and

single secondary memory space

– used for distributed file system

Characteristics of Modern

Operating Systems

• Object-oriented design

– used for adding modular extensions to a small kernel

– enables programmers to customize an operating

system without disrupting system integrity