Lesson 1: Operating System Basics

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Lesson 1: Operating System Basics



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What is an Operating System?

OS = Operating System

A program that controls the execution of application programs.

An interface between applications and hardware.

Makes the computer more convenient to use



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What is an Operating system?

Manages the resources of a computer and controls the way they are used.

Allows resources to be used in an efficient manner.

Examples of OS’s?



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Where are OS’s used?

In more and more places! Desktop and Server Computers DOS + Windows 95/98/ME

Windows NT/2000/XP Free Unix variants: Linux, FreeBSD,

NetBSD, etc. Commercial Unix variants: Solaris, HP-

UX, AIX, etc.



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MacOS Some Game Consoles Xbox: Cut-down Windows 2000 Personal Digital Assistants (PDAs) PalmOS Windows CE Windows Mobile



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Embedded Linux Mobile Phones Symbian OS Windows Mobile Cars (fancy ones)



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In the future also: Digital Cameras (fancy ones) MP3 Players (iPods, etc.) Refrigerators! Others?



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Layers of a Computer System



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Services And System Calls

User Program(requests service) from

kernel

UNIX system kernel

(provides services) toThe user

Service,dataand

Status returned

Type,Data details Are sent

Services offered and system calls



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Services Provided by the OS

Program execution Access to Input/Output (I/O)

devices Disks, screens, keyboards, mice Printers, cameras, speakers, etc.



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Controlled access to files System access Sometimes: Program development Compilers, editors and debuggers Error detection and response Internal and external hardware errors Memory errors



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Device failures Software errors Arithmetic overflow Division by zero Access to forbidden memory locations

(why?) Operating system cannot grant request

of application



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Operating System as Software

The OS functions the same way as ordinary computer software It is a program that is executed … … but it has special privileges The OS relinquishes control of the processor to execute other

programs



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Provide a user interfaceProvide a user interface Run programsRun programs Manage hardware devicesManage hardware devices Organized file storageOrganized file storage

Functions of Operating Systems



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Types of Operating Systems

Real-time operating systemReal-time operating system Very fast small OS Built into a device Respond quickly to user input MP3 players, Medical devices



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Single user/Single tasking OSSingle user/Single tasking OS One user works on the system Performs one task at a time MS-DOS and Palm OS Take up little space on disk Run on inexpensive computers



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Single user/Multitasking OSSingle user/Multitasking OS User performs many tasks at

once Most common form of OS Windows XP and OS X Require expensive computers Tend to be complex



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Multi user/Multi tasking OS



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Providing a User Interface

User interfaceUser interface How a user interacts with a

computer Require different skill sets



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Providing a User Interface

Graphical user interface (GUI)Graphical user interface (GUI) Most common interface

Windows, OS X, Gnome, KDE Uses a mouse to control objects Uses a desktop metaphor



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Contd:

Shortcuts open programs or documents

Open documents have additional objects

Task switching Dialog boxes allow directed

input



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Graphical User Interface



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Running Programs

Many different applications supportedMany different applications supported System callSystem call

Provides consistent access to OS features

Share information between programsShare information between programs Copy and paste Object Linking and Embedding



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Managing Hardware

Programs need to access Programs need to access hardwarehardware

InterruptsInterrupts CPU is stopped Hardware device is accessed

Device drivers control the Device drivers control the hardwarehardware



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Organizing Files and Folders

Organized storageOrganized storage Long file namesLong file names Folders can be created and Folders can be created and

nestednested All storage devices work All storage devices work

consistentlyconsistently



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Enhancing an OS

UtilitiesUtilities Provide services not included

with OS Goes beyond the four functions Firewall, anti-virus and

compression Prices vary



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Enhancing an OS

Backup softwareBackup software Archives files onto removable

media Ensures data integrity Most OS include a backup

package Many third party packages exist



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Backup Software



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Enhancing an OS

Anti-virus softwareAnti-virus software Crucial utility Finds, blocks and removes

viruses Must be updated regularly McAfee and Norton Anti-Virus



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Enhancing an OS

FirewallFirewall Crucial utility Protects your computer from

intruders Makes computer invisible to

hackers Zone Labs is a home firewall Cisco sells hardware firewalls



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UNIX

Unix is a multi-user, multi-tasking Unix is a multi-user, multi-tasking operating system.operating system.

You can have many users logged You can have many users logged into a system simultaneously, each into a system simultaneously, each running many programs. running many programs.

It's the kernel's job to keep each It's the kernel's job to keep each process and user separate and to process and user separate and to regulate access to system regulate access to system hardware, including cpu, memory, hardware, including cpu, memory, disk and other I/O devices. disk and other I/O devices.



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History of UNIX

First Version was created in Bell First Version was created in Bell Labs in 1969.Labs in 1969.

Some of the Bell Labs programmers Some of the Bell Labs programmers who had worked on this project, who had worked on this project, Ken Thompson, Dennis Ritchie, Ken Thompson, Dennis Ritchie, Rudd Canaday, and Doug McIlroy Rudd Canaday, and Doug McIlroy designed and implementeddesigned and implemented



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History of UNIX

the first version of the Unix File the first version of the Unix File System on a PDP-7 along with a System on a PDP-7 along with a few utilities. It was given the name few utilities. It was given the name UNIX by Brian Kernighan. UNIX by Brian Kernighan.

00:00:00 Hours, Jan 1, 1970 is time 00:00:00 Hours, Jan 1, 1970 is time zero for UNIX. It is also called as zero for UNIX. It is also called as epoch.epoch.



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History of UNIX

1973 Unix is re-written mostly 1973 Unix is re-written mostly in C, a new language developed in C, a new language developed by Dennis Ritchie. by Dennis Ritchie.

Being written in this high-level Being written in this high-level language greatly decreased the language greatly decreased the effort needed to port it to new effort needed to port it to new machines. machines.



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History of UNIX

1977 There were about 500 1977 There were about 500 Unix sites world-wide. Unix sites world-wide.

1980 BSD 4.1 (Berkeley 1980 BSD 4.1 (Berkeley Software Development) Software Development)

1983 SunOS, BSD 4.2, System 1983 SunOS, BSD 4.2, System V V



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History of UNIX

1988 AT&T and Sun 1988 AT&T and Sun Microsystems jointly develop Microsystems jointly develop System V Release 4 (SVR4). System V Release 4 (SVR4). This later developed into This later developed into UnixWare and Solaris 2. UnixWare and Solaris 2.

1991 Linux was originated.1991 Linux was originated.



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What is LINUX

Linux is a free Unix-type operating Linux is a free Unix-type operating system originally created by Linus system originally created by Linus Torvalds with the assistance of Torvalds with the assistance of developers around the world. developers around the world.

It originated in 1991 as a personal It originated in 1991 as a personal project of Linus Torvalds, a Finnish project of Linus Torvalds, a Finnish graduate student.graduate student.



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What is LINUX

The Kernel version 1.0 was The Kernel version 1.0 was released in 1994 and today the released in 1994 and today the most recent stable version is 2.6.9most recent stable version is 2.6.9

Developed under the Developed under the GNU General Public License , the the source code for Linux is freely source code for Linux is freely available to everyone. available to everyone.



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LINUX Distributions

Mandrake: Mandrake: http://http://www.mandrakesoft.comwww.mandrakesoft.com//

RedHat: RedHat: http://http://www.redhat.comwww.redhat.com//

Fedora: Fedora: http://http://fedora.redhat.comfedora.redhat.com//

SuSE/Novell: SuSE/Novell: http://http://www.suse.comwww.suse.com//

Debian: Debian: http://http://www.debian.orgwww.debian.org//



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Red Hat

Red Hat Enterprise Linux is a Red Hat Enterprise Linux is a Enterprise targeted Operating Enterprise targeted Operating System. It based on mature Open System. It based on mature Open Source technology and available at Source technology and available at a cost with one year Red Hat a cost with one year Red Hat Network subscription for upgrade Network subscription for upgrade and support contract.and support contract.



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UNIX Structure



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Components of a Linux System

Like most UNIX implementations, Like most UNIX implementations, Linux is composed of three main Linux is composed of three main bodies of code; the most important bodies of code; the most important distinction between the kernel and distinction between the kernel and all other componentsall other components



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Kernel

Portion of operating system that is always in main memory

Contains most-frequently used functions

Also called the nucleus Good performance of the kernel is

very important



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Components of a Linux System (Cont.)

The kernel is responsible for The kernel is responsible for maintaining the important maintaining the important abstractions of the operating abstractions of the operating system.system.



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Kernel code executes in kernel mode with full access to all the physical resources of the computer.

All kernel code and data structures are kept in the same single address space.



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The system libraries define a The system libraries define a standard set of functions through standard set of functions through which applications interact with the which applications interact with the kernel, and which implement much kernel, and which implement much of the operating-system of the operating-system functionality that does not need the functionality that does not need the full privileges of kernel code.full privileges of kernel code.



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Shell

Shell is the command interpreter.Shell is the command interpreter.

It is a interface between a user and It is a interface between a user and the system. the system.

The kernel activates an interactive The kernel activates an interactive program called shell for each user program called shell for each user logged into the system. logged into the system.



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Shell

Shells provide a way to separate Shells provide a way to separate users or tasks from each other.users or tasks from each other.

Kernel maintains a unified overall Kernel maintains a unified overall control. control.

Shell provides a prompt like $ or %.Shell provides a prompt like $ or %. This is called the command line This is called the command line

interface of the shell. interface of the shell.



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Shell

The user can type any valid The user can type any valid UNIX/Linux command.UNIX/Linux command.

Can run a shell script and press Can run a shell script and press enter to intimate the shell about enter to intimate the shell about the task to perform.the task to perform.

The shell interprets the typed The shell interprets the typed command and searches a command and searches a predefined path for the executable predefined path for the executable file by the name of the command file by the name of the command typed. typed.



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Shell

It checks the syntax of the It checks the syntax of the commands and if all is fine, starts commands and if all is fine, starts the corresponding executable the corresponding executable running and goes into waiting mode. running and goes into waiting mode.

After the command finishes After the command finishes executing, it exits and control is executing, it exits and control is returned to the shell. returned to the shell.



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Shell

A shell prompt is returned to the A shell prompt is returned to the user. user.

Actual fetching and returning of Actual fetching and returning of data at the request of the shell is data at the request of the shell is done by the kernel.done by the kernel.



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Before Operating Systems…

Serial Processing No operating system Machines run from a console with

display lights and toggle switches, input device, and printer.

Schedule time



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Before Operating Systems…

Setup included loading the compiler, source program, saving compiled program, and loading and linking.



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Uniprogramming

Uniprogramming Processor must wait for I/O

instruction to complete before preceding.



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Uniprogramming

But! Processors are much faster than I/O devices… inefficient use of CPU



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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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Example Effects

Uniprogramming MultiprogrammingUniprogramming Multiprogramming

Processor use 22% Processor use 22% 43%43%

Memory use Memory use 30% 67% 30% 67%

Disk use 33% Disk use 33% 67% 67%

Printer use Printer use 33% 33% 67% 67%

Elapsed time 30 min. Elapsed time 30 min. 15 min. 15 min.

Throughput rate 6 jobs/hr 12 jobs/hrThroughput rate 6 jobs/hr 12 jobs/hr

Mean response time 18 min. 10 min.Mean response time 18 min. 10 min.



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Achievements in OS Research

Processes Memory management Information protection and

security Scheduling and resource

management System structure



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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

executed on a processor A unit of activity characterized by a

single sequential thread of execution a current state an associated set of system resources



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Processes

Consists of three components An executable program, i.e., some

code Associated data needed by the

program Execution context of the program



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Processes

All information the operating system needs to manage the process.

e.g., who owns the process, which priority does it have, what resources does it currently ‘own’.



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OS Support for Processes

Creating, destroying, starting, stopping,setting priorities, …

Process synchronisation Semaphores (wait/signal) Monitors Deadlock detection Inter-process communication Shared memory



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Processes in Linux



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Modern Operating Systems

Multithreading• Each process is divided into threads that can

run simultaneously.

Thread• Dispatchable unit of work• Executes sequentially and is interruptible.

A process is a collection of one or more threads



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Symmetric multiprocessing. There are multiple processors. These processors share same main

memory and I/O facilities. All processors can perform the

same functions.



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Distributed operating systems

• Provides the illusion of a single main memory and single secondary memory space.

• Distributed shared memory• Distributed file systems



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Example OS: PalmOS

•Used for PalmPilot PDAsand successors.• Multitasking sincePalmOS 5.• CPUs: Intel XScale,Texas InstrumentsOMAP, MotorolaDragonball MX• Wireless: 802.11b,Bluetooth, GSM, CDMA• 320×320+ displays Good battery utilisation



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Example OS: SymbianOS

•Designed for mobile phones• Gives access to graphics, multimedia, networking, telephony, crypto, PC connectivity, etc.



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The OS Wars

Why is the OS such a big deal?• Windows vs Linux vs Mac• Symbian vs PalmOS vs Windows Mobile

IncompatibilitiesIncompatibilities• OS’s have different interfaces.• programs must be written differently.• applications for one OS don’t run on another.

Tendency to bloatware• Applications tend to move into the OS• Internet Explorer, Media Player, Search?



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Security: Windows vs Linux

Windows Family Developed from DOS Originally single-user machines No network few threats

Linux Developed from Unix Originally multi-user networked servers Designed to withstand with security threats

from the beginning



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THANK YOUTHANK YOU



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Lesson 1: Operating System Basics