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Course : Operating Systems

Lecturer: Noha A. Yousri

Contact information: [email protected]

Text Book:Operating Systems, by Deitel, Deitel and Choffnes, 3rd

edition.

References:

Operating Systems, Internals and Design Principles, byWilliam Stallings, 3rd edition.

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Course Objectives:

-What is an Operating System

-Understanding the major components of an OS

(Theoretically and practically)-Case Studies

Grading Scheme:

Total marks: 125

Final exam: 90

Years work: 35

(Midterm + sheets, quizes and programming assignments)

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Course Contents:

-Introduction (Deitel Ch. 1, Stallings Ch.2)

-Hardware and Software

-Processes Concepts-Thread Concepts

-Concurrent Programming

-Memory Management

-Disk Scheduling

-File management

-Case studies: linux, Windows XP

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Lecture 1

Introduction

What is an OS?

History : Evolution of an OS

Core components of an OS

OS goals (characteristics) OS Architecture

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Applications

Operating System

Hardware

User(s)What is an OS?

OS is the software that controls the hardware

OS is the layer between applications and H.W

OS is a resource manager

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How a user interacts with an OS?

-One or more user applications

-Shell or command interpreter

--Text based

--GUI

What is a kernel?

S.W containing core components of OS

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History : Evolution of Operating Systems

Single Interactive User

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-Single Interactive User (Serial processing )

User uses switches/card reader for input,

User examines cause of error from

registers/memory

Problems:

Wasting an expensive resource (e.g. Reservingtime more than needed )

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Single-job batch streaming:

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-Single-job batch streaming:A batch of jobs are ready, read a job at a

time,Job either uses CPU or I/O

Job cant make CPU and I/O busy at the

same time

(A job is either CPU bound or I/O bound)

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-Multiprogramming:

Several jobs can execute by sharing CPU,and I/O

Switch from a job using I/O to another job

Manage resources, security issues, .

-Interactive users : do not wait for batch outputs

-Time sharing systems: for multiple users, eachrunning a job

Interactive time sharing

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Interactive time sharing

Multiple Interactive UsersMultimode:

Batch Processing, Real Time systems

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Following are consequent evolutions:

file system : Storing users files on the system

Prioritized scheduling , and Distinguishing Jobs:Doing important jobs first:

-Real time systems need fast response time.

(highest level service)-Interactive applications (lower level service)

-Batch streaming (lowest level: but reasonable

delay)

Resource management: disk quota for each user.

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Communication between computers:

Transferring data and information betweenpeople,

LAN is now feasible

Networking Issues?Security Issues?

Graphical user interface :permitted multiple applications (process) to work

concurrently

Distributed systems: (appeared withcommunication)

to exploit the resources that can be distributed atseveral places

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Embedded systems:

e.g. PDA (personal digital assistant), handheldcomputers, etc

operating systems should consider issues as:

power management, user friendly interface, limitedresources (memory, etc)..

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Period of 1990s

-Hardware performance improved

-shift towards distributed computing accelerated

-Object technology:Object Oriented Operating Systems (e.g. BeOS)

-Open Source Movement

-open source software (code available free of charge)

-Graphical User Interface

-Enhanced, more user friendly

-Plug and Play technology

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Period of 2000 & Beyond

-Middleware : acts as a courier that passesmessages between components or applications (e.g.

web server and database)*

-Web Services: provides a set of applications thatother applications can invoke (helps enhance

distributed computing)-Concurrent programming languages

-Massive Parallelism

*Middleware is computer software that connects software components or applications. The software

consists of a set of enabling services that allow multiple processes running on one or more machines tointeract across a network. It sits "in the middle" between application software working on differentoperating systems (wikipedia definition)

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Lecture #2

(Continue Introduction)

Operating System Environment

Operating System Components

Operating System Goals

Operating System Architecture

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Operating System Environments

-Embedded systems

-provide functionality to deal with specialized

resources (e.g. limited storage, etc..)e.g. cell phones, PDAs

-Real Time systems

Enable processes to respond immediatelyto a

criticalevent

e.g. autopilot feature of an aircraft

-Business critical systems

-Fast response time to purchasing transacions

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Virtual Machines

-Software implementation of a computer

-Executes as an application on top of native OS

Applications:

-Allows multiple OSs to operate concurrently

-Emulation: Mimics functionality of S.W or

H.W not present in system-Portability

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2004, Deitel & Associations, Inc, All Rights reserved

Virtual Machine


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What are the core components ofan

operating system?

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Revise that:

OS evolved to fill new roles

Evolution:

No OS

Multiprogramming

Time sharingPersonal Computer

Distributed System

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Memory

I/O

CPU

P1

P2

P3

P4 P5

Infer the core componentsfrom the diagram.

What are the main elements?

Storage

Processes

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Think about these:

- When Nprocesses are ready, which process executesfirst? Why?

-Can a process access any address in memory? How is

memory shared among different processes?

-When the total memory is occupied, what otherresources can be used to extend it? How?

-Sometimes, processes should tell one another abouttheir status when they share a resource, how can this bedone?

-Processes compete to send a request to I/O (e.g. disk),which process goes first?

-How can some data be written to the disk? Allocated

certain space on disk? Accessed from disk?

OS Components

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Multiprogramming: applications execute concurrently

When N processes are ready, which process executes first?Why?

1- Processor Scheduler

When does a process execute?

For how long a process executes?

Which processor executes the process?

solution

OS Components

OS C

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Processes will compete for resources e.g. memory

One process should not interfere with the space

allocated to another processes or to space allocatedto the OS

When the memory is full, what can be done to

execute a process demanding large space?

2-Memory Manager

When is memory allocated to a process?

How is memory is allocated to it?

How to manage a full memory?

solution

OS Components

OS C t

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When a process wants to access I/O (most commonly disk),

what happens?

A process issues a system call to the OS.

A system call is handled by a device

manager ( a S.W that interacts with H.W)

Problem!!!

Secondary storage much slower than processor and

main memory solution

3-I/O Manager

Service I/O requests from/to H.W devices

e.g. Disk Scheduler: maximize performance,

Minimize time process waits for I/O

OS Components

OS C t

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solution

Files are named collections of data

A Need for organizing them on storage device

Need an interface to access data on the

storage device

4- File System Manager

OS Components

OS Components

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Can processes (or threads) cooperateto finish a job?

How can they coordinate and be able to communicate,share datawhile concurrently executing?

solution

5- Inter Process Communication (IPC)

-Processes communicate through messages

-Synchronization is required to share data

OS Components

OS Components

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1-Processor Scheduler

2-Memory Manager

3-I/O Manager

4-File Manager

5-Inter Process Communication

OS Components

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Characteristics (& Goals) of an OS

-Maximize amount of work a processor can

complete, given a time period

i.e. Maximize throughput-Minimize time spent for a certain service

i.e Minimize turn around time

Efficiency

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System should not fail on isolated H.W/S.W errors

if it fails, it should prevent damage/loss ofwork or data

Robustness

FaultTolerance

Reliability

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When resources are added to the system , shallthey be fully utilized?

e.g. when more processors are added

processing capacity should increase

w.r.t to the number of processes

ScalabilityAbility to use

resources as

they are added

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When new technologies appear, what happens toan OS?

Can an OS extend to adaptto new technologies?

Extensibility extend to adaptto new tech.

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-Different hardware configurations??

Portability

Operate on

many H.Wconfigurations

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Users should have certain authorization limits to

protect a system against interference/hacking..etc

Security

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Interactivity


Quick Response

Detect errors

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Easy to use

Support large set of applications

Use standard user interface (friendly one)

Usability

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Interactivity

Security

Robustness

Extensibility

Efficiency

Scalability

Portability

Usability

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Operating System Architecture:

-Monolithic

-Layered

-Micro Kernel

-Network and Distributed OS

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1-Monolithic

-Earliest and most common architecture

-Every component is inside the kernel anddirectly communicates with any other componentusing function calls

-Kernel executes with unrestricted access to the

computer system

-e.g. linux

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Monolithic Architecture:

Advantages:

Highly efficient : direct intercommunication

between components

Disadvantages:

-Difficult o isolate source of bugs or errors

-Susceptible to damage due to unrestricted

access to system


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OS is more complex, and larger, lead to:

2- Layered Architecture

-Group components according to functionalityinto layers

-Each layer communicate with the layer above it

or below it

-lower layers provide services to higher ones

using an interface that hides implementation

E.g. WinXP (some level of layering)

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Layered Architecture:

Advantages:

More modular than monlithic

Easy to modify a layer without modifying

other layers

Reusable

Hiding complexities, and using standard

interface

Structured and consistent

Simplifies validation, debugging

L d A hit t

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Layered Architecture:

Disadvantages:

A users request passes through many layers

before service Additional methods needs to pass data from

one layer to the next

performance degrades (compared to

monolithic architecture)

Unrestricted access to system

Susceptible to damage from malicious code

O i S A hi

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3-MicroKernel

-Keep kernel small and scalable

-Limit no. of services to

e.g.: low level memory management

Interprocess communication

Basic Process synchronization

-Other services execute outside kernel with lowerprivilege

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MicroKernel

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MicroKernel

Advantages:

-High degree of modularity making them:

-Portable, Scalable and Extensible

-One or more components failure does not cause

OS to fail

Disadvantages:

-High modularity level causes

increased level of intermodule communication

performance degradation

Operating S stem Architect re

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4-Networked and Distributed OS

Network OS:

Enables its processes to access resources(e.g. files) that reside on independent computers

Structure based on client/server modelClients request resources

Server respondsDistributed OS:

Single OS that manages resources on more than

one computer

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Client/server Networked OS


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