Lecture 16

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CS1010 Introduction to Computing

Lecture 16

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TODAY’s LECTURE

• _The_{role of operating system}_{in a computing}

environment.

• _The_{various functions}_{that an operating}

system performs?

• _The_{main components}_{of operating system.}

• _Various_types_{of operating systems.}

• _The_{role of operating system}_{in a computing}

environment.

• _The_{various functions} _{that an operating}

system performs?

• _The_{main components}_{of operating system.}

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Why Have OSes

?

Why Have OSes

?

1. User/programmer convenience

2. Greater resource utilization

1. User/programmer convenience

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THE ROLE OF AN OS

• _The_{1st program}_{that runs when a typical computer} is turned ON, and the last one to finish running

when the computer is turned OFF

• _It_{manages the HW and SW resources}_{of the}

computer system, often invisibly. These include the processor, memory, disk drives, etc.

• _{It provides a}_simple_,_{consistent way for}

applications to interact with the HW without having to know all the details of the HW

• _The_{1st program}_{that runs when a typical computer} is turned ON, and the last one to finish running

when the computer is turned OFF

• _It_{manages the HW and SW resources}_{of the}

computer system, often invisibly. These include the processor, memory, disk drives, etc.

• _{It provides a}_simple_, _{consistent way for}

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Advantage for App. Developers

•_{App developers}_{do not need to know}_{much about}

the HW while they are developing their app

•_They_{just develop with a particular OS in mind}_{. If}

the OS runs on many types of computers having different HW configurations, so will the app –

without making any HW-specific modifications in the app SW. The OS hides the HW differences

from the app

•_{App developers}_{do not need to know}_{much about}

the HW while they are developing their app

•_They_{just develop with a particular OS in mind}_{. If}

the OS runs on many types of computers having different HW configurations, so will the app –

without making any HW-specific modifications in the app SW. The OS hides the HW differences

from the app

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• _{Applications interact with}_OS_,_OS_{talks with}

hardware for a particular task that is need to be done.

• _{Is it possible to bypass the OS?}

• _{Is it possible to have a computer with no OS just}

application is running?

• _{Yes, many computers in the world}_{, which have}

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Are OS’es Essential?

• _{No. If a computer has been designed for limited} functionality (e.g. it runs just a single program all the time as in a automatic clothes washing

machine), it does not require a traditional OS

• _In_{limited-functionality computers}_{, an}_{OS just}

adds to the overhead unnecessarily, which

impedes the computer’s performance

• _{In these situations, the}_{required parts}_{of the OS} are integrated into the only program that is going to run

• _{No. If a computer has been designed for limited} functionality (e.g. it runs just a single program all the time as in a automatic clothes washing

machine), it does not require a traditional OS

• _In_{limited-functionality computers}_{, an OS just} adds to the overhead unnecessarily, which

impedes the computer’s performance

• _{In these situations, the required parts of the OS} are integrated into the only program that is going to run

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In the beginning …

• _A_{single user ran a single program}_{ran on a single}

computer – there was no need for an OS

• _{Then came computer operators who ran}_multiple programs for multiple users one after the other – still, no need for an OS

• _Later_{computers became powerful}_{, & became able to run}

multiple programs, simultaneously. That’s when the need for OS’es arose for:

– _{Managing the resources}_{of the computers efficiently}

– _Making_{use of computers convenient}_{for users/programmers}

• _A_{single user ran a single program}_{ran on a single}

computer – there was no need for an OS

• _{Then came computer operators who ran}_multiple

programs for multiple users one after the other – still, no need for an OS

• _Later_{computers became powerful}_{, & became able to run}

multiple programs, simultaneously. That’s when the need for OS’es arose for:

– _{Managing the resources}_{of the computers efficiently}

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CORE TASK OF AN OS

1. Processor management

2. Memory management

3. Device management

4. Storage management

5. Application Interface

6. User Interface

1. Processor management

2. Memory management

3. Device management

4. Storage management

5. Application Interface

6. User Interface

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Processor Management

• _Various_{programs compete for the attention}_of

the uP(microprocessor) for their own purposes

• _The_{OS plays the role of the honest referee}_,

making sure that each app gets the necessary

attention required for its proper execution

• _{It tries to}_{optimally manages the limited}

processing capacity of the uP to the greatest good of all the users & apps

• _Various_{programs compete for the attention}_of

the uP(microprocessor) for their own purposes

• _The_{OS plays the role of the honest referee}_,

making sure that each app gets the necessary

attention required for its proper execution

• _{It tries to}_{optimally manages the limited}

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Memory Management

• _{Straight forward for}_{a single-user, single tasking}

• _{Each app must have}_{enough private memory}_in which to execute

• _{App can neither}_{run into the private memory space} of another app, nor be run into by another app

• _{Different types}_{of memory (e.g. main, cache) in the} system must be used properly, so that each app

can run most effectively

• _{Straight forward for}_{a single-user, single tasking}

• _{Each app must have}_{enough private memory}_in which to execute

• _{App can neither}_{run into the private memory space} of another app, nor be run into by another app

• _{Different types of memory (e.g. main, cache) in the}

system must be used properly, so that each app can run most effectively

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Storage Management

• _{The OS manages storage through one of its}

sub-modules, the File Manager

• _A_{file system}_{is a collection of directories,}

subdirectories, and files organized in a logical order

• _{File manager}_{maintains an index}_{of the filenames &} where they are located on the disk

• _{File manager make it easy to find}_{the required file} in a logical and timely fashion

• _{The OS manages storage through one of its} sub-modules, the File Manager

• _{A file system is a collection of directories,}

subdirectories, and files organized in a logical order

• _{File manager} _{maintains an index} _{of the filenames &} where they are located on the disk

• _{File manager make it easy to find the required file}

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Device Management

• _{Applications talk to devices}_{through the OS}

and OS talks to and manages devices through Device Drivers

• _Example:_{When we}_{print to a laser printer}_,

we do not need to know its details. All we do is to tell the printer device driver about what needs to be printed and it takes care of the details

• _{Applications talk to devices}_{through the OS}

and OS talks to and manages devices through Device Drivers

• _Example:_{When we}_{print to a laser printer}_,

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Application Interface

• _App_{developers do not need to know}_{much about} the HW, especially the uP, while they are developing their app

• _{The OS provides all}_{apps with a straight-forward}

and consistent interface to the HW

• _Example:_An_{app uses the OS to store data on the}

disk drive. For that, the app does not need to know about the exact physical characteristics of that

drive; it just tells the OS to do that through the app interface, and the OS takes cares of all the details of the task

• _App_{developers do not need to know}_{much about} the HW, especially the uP, while they are developing their app

• _{The OS provides all apps with a straight-forward} and consistent interface to the HW

• _{Example: An}_{app uses the OS to store data on the}

disk drive. For that, the app does not need to know about the exact physical characteristics of that

drive; it just tells the OS to do that through the app interface, and the OS takes cares of all the details of the task

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User Interface

• Users communicate with the computer using a

consistent user interface provided by the OS

• _{This UI can be a}_{command-line interface}_{in which a user}

types in the commands. Example:

copy a:/file1.html c:/file1.html

• _{Or, it can be a}_{graphical UI}_{, where}_{Windows, Icons,}

Menus, and a Pointing device (such as a mouse) is used to receive and display information. Example:

With the help of the mouse, drag file1.html from drive a to drive c

• _{Users communicate}_{with the computer using a}

consistent user interface provided by the OS

• _{This UI can be a}_{command-line interface}_{in which a user}

types in the commands. Example:

copy a:/file1.html c:/file1.html

• _{Or, it can be a graphical UI, where}_{Windows, Icons,}

Menus, and a Pointing device (such as a mouse) is used to receive and display information. Example:

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Icons

Start menu Start button Taskbar

Desktop

Dialog box

Program running in

a window

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Or, icons can be double-clicked to launch programs. The Windows start

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OS COMPONENTS

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Kernel

Command Interpreter

(Shell) File Manager Device

Manager

GUI

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Kernal

• _The_heart/brain_{of the OS}

• _{Responsible for all the}_{essential operations}

like basic house keeping, task scheduling, etc. Also contains low-level HW interfaces

• _{Size important}_{, as it is memory-resident} • _The_heart/brain_{of the OS}

• _{Responsible for all the}_{essential operations}

like basic house keeping, task scheduling, etc. Also contains low-level HW interfaces

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Types of OS’es

• _{Classification w.r.t. the}_{type of computers}_they

run on and the type of applications they support

– _Real-Time_{Operating System (RTOS)} – _{Single-User, Single Task}

– _{Single-User, Multi-Tasking} – _Multi-User

• _{Classification w.r.t. the}_{type of computers}_they

run on and the type of applications they support

– _Real-Time_{Operating System (RTOS)}

– _{Single-User, Single Task}

– _{Single-User, Multi-Tasking}

– _Multi-User

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RTOS (1)

• _{Used to run}_{computers embedded}_in

machinery, robots, scientific instruments and industrial systems

• _{Typically, it has}_{little user interaction}

capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use

• _Examples:_{Wind River, QNX, Real-time Linux,}

Real-time Windows NT

• _{Used to run}_{computers embedded}_in

machinery, robots, scientific instruments and industrial systems

• _{Typically, it has}_{little user interaction}

capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use

• _Examples:_{Wind River, QNX, Real-time Linux,}

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RTOS (2)

• _{An important part of an RTOS is}_{managing the}

resources of the computer so that a particular operation executes in precisely the same

amount of time every time it occurs

• _{In a complex machine,}_{having a part move}

more quickly just because system resources are available may be just as CATASTROPHIC as having it not move at all because the system was busy

• _{An important part of an RTOS is}_{managing the}

resources of the computer so that a particular operation executes in precisely the same

amount of time every time it occurs

• _{In a complex machine,}_{having a part move}

more quickly just because system resources are available may be just as CATASTROPHIC as having it not move at all because the system was busy

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Single-User, Single Task

• _{OS’es designed to manage the computer so that}

one user can effectively do one thing at a time

• _The_{Palm OS}_{used in many palmtop computers}

(PDA’s) is an example of a single-user, single-task OS

• _{OS’es designed to manage the computer so that}

one user can effectively do one thing at a time

• _The_{Palm OS}_{used in many palmtop computers}

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Single User, Multi-Tasking

• _Most_popular_OS

• _{Used by}_{most all PC’s}_{and Laptops}

• _Examples:_{Windows, Mac OS, Linux}

• _{Lets a single user}_{interact with several}

programs, simultaneously

• _Most_popular_OS

• _{Used by}_{most all PC’s}_{and Laptops}

• _Examples:_{Windows, Mac OS, Linux}

• _{Lets a single user}_{interact with several}

programs, simultaneously

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Multi-User

• _{A multi-user OS allows many users to take} advantage of the computer's resources, simultaneously

• _{The OS must make sure that the}_{requirements of}

the various users are balanced, and that the

programs they are using each have sufficient and separate resources so that a problem with one user doesn't affect any of the other users

• _Examples:_{Linux, Unix, VMS and mainframe OS’es,} such as MVS

• _{A multi-user OS allows many users to take} advantage of the computer's resources, simultaneously

• _{The OS must make sure that the requirements of} the various users are balanced, and that the

programs they are using each have sufficient and separate resources so that a problem with one user doesn't affect any of the other users

• _{Examples: Linux, Unix, VMS and mainframe OS’es,}

such as MVS

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Another Way of Classifying

Uni-processor OS’es

Designed to schedule tasks on a single uP only

Example: DOS

Multi-processor OS’es

Can control computers having multiple uPs, at times 1000’s of them

Example: Current versions of Windows, Mac OS, Linux, Solaris

Uni-processor OS’es

Designed to schedule tasks on a single uP only

Example: DOS

Multi-processor OS’es

Can control computers having multiple uPs, at times 1000’s of them

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How many different OS’es are there?

• _100’s

• _{OS’es from the}_{Windows family}_{dominate the}

desktops and run on millions of PC’s

• _{OS’es from the}_{Unix family}_{(Unix, Linux, etc) are}

quite popular on servers

• _{There are}_{hundreds more}_{. Some designed for} mainframes only. Some for embedded

applications only.

• _100’s

• _{OS’es from the}_{Windows family}_{dominate the}

desktops and run on millions of PC’s

• _{OS’es from the}_{Unix family}_{(Unix, Linux, etc) are}

quite popular on servers

• _{There are}_{hundreds more}_{. Some designed for}

mainframes only. Some for embedded

applications only.

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Comparing Popular OS’es

OS HW Stability Cost Apps. Support Security Popularity

Windows

(GUI) PC Poor $300 Huge no. OK Poor Amazing

Mac OS

(Shell/GUI) Mac Good $60 Many OK Good Low

Linux

(Shell/GUI) Many Good Low Many Variable Good Low

Unix

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• _{UNIX is the oldest operating system used on}

PCs.

• _{UNIX was the first multi-user, multiprocessor,}

multitasking operating system available for use on PCs.

• _{Most versions of UNIX use a command-line}

interface, but some versions offer a GUI.

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• _{DOS dominated the operating system market}

during the 1980s.

• _{DOS is a single-user OS that supports only 640}

KB of memory.

• _{DOS features a command-line interface, and}

does not support multitasking or multiprocessing.

• _{Because DOS provides no interface restrictions,}

DOS applications can look and function differently.

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• _{The Macintosh OS supports the graphical}

nature of the Macintosh computer.

• _{The Mac OS brought the first truly graphical}

user interface to consumers.

• _{The Mac OS also brought interface conformity}

to the desktop. All applications running under the Mac OS, therefore, provided the same

"look and feel" to the user.

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• _{Windows 3.0, 3.1, and 3.11 are called the}

Windows 3.x family.

• _{Windows 3.x brought a GUI and multitasking}

capabilities to PCs running DOS.

• _{Windows 3.x is an operating environment}

because it ran on top of DOS, which was the actual OS.

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• _{OS/2 Warp was the first true GUI-based operating}

system for Intel-based PCs.

• _{OS/2 is a multitasking OS that provides support}

for networking and multiple users.

• _{It was the first PC OS to feature built-in speech}

recognition capabilities.

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• _{Microsoft's Windows NT was meant as a}

replacement for DOS, but was too

resource-intensive to work on most PCs at the time of its release.

• _{Microsoft issued two versions of Windows NT}

—Windows NT Workstation and Windows NT Server.

• _{NT is a very powerful and robust OS, resistant}

to system crashes.

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• _{Windows 95 was Microsoft's first true}

GUI-based, 32-bit operating system for Intel PCs.

• _{Windows 95 supports multitasking and can}

run older DOS and Windows 3.x programs.

• _{Windows 98's features include advanced}

Internet capabilities, an improved user interface, and enhanced file system performance, among others.

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• _{Linux is a recently developed version of UNIX,}

which is available for free or at a very low cost from various sources.

• _{Linux is a very powerful 32-bit OS that supports}

multitasking, multiple users, networking, and virtually any application.

• _{Linux can run on nearly any type of computer.}

• _{Because of its power and openness, Linux is}

attracting many users, including students,

teachers, Internet service providers, and others.

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• _{Windows 2000 features the same interface and}

features of Windows 98, with the file system, networking, power, and stability of Windows NT.

• _{Several versions of Windows 2000 are}

available, each targeting a specific user or computing environment, from home PCs to large enterprise networks.

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What have we learnt today?

• _The_role_{of the OS in a computing}

environment

• _{The various}_functions_{that an OS performs}

• _{The main}_components_{of an OS}

• _Various_types_{of OS’es}

• _The_role_{of the OS in a computing}

environment

• _{The various}_functions_{that an OS performs}

• _{The main}_components_{of an OS}