Operating System: functions, components, types of operating systems

<< COMPUTER SOFTWARE: Operating Systems, Device Drivers, Trialware

Forms on Web pages, Components of Forms, building interactive Forms >>

Introduction to Computing CS101

LESSON 11

OPERATING SYSTEMS

Focus of the last lecture: Computer SW

We found out about the role SW plays in a computing environment

We learned to distinguish between SW belonging to the system & application categories

Also discussed the different types of SW licenses:

Proprietary

Free

Open source

Shareware

Trialware

Learning Goals for Today

The role of the operating system in a computing environment

The various functions that an operating system performs

The main components of an operating system

Various types of operating systems

11.1 Why Have OSes?

User/programmer convenience

Greater resource utilization

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

Advantage for App. Developers

Application 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

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 the only

program that is going to run.

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

Introduction to Computing CS101

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

11.2 Core Tasks of an OS

Processor management

Memory management

Device management

Storage management

Application Interface

User Interface

Processor Management

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

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.

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

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

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:

Introduction to Computing CS101

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

11.3 OS Components

Error!

Device

Manager

File

Manager

Kernel

Loader

Command

Interpreter

(Shell) GUI

11.4 Kernel

The heart 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

11.5Types 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

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

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

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

Introduction to Computing CS101

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

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

11.6 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

11.7 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.

11.8 Comparing Popular OS'es

Stability

Cost

Apps.

Support

Security

Popularity

Huge

Windows

Poor

$300

Poor

Amazing

no.

(GUI)

Mac OS

Mac

Good

$60

Many OK

Good

Low

(Shell/GUI)

Linux

Many Good

Low

Many Variable

Good

Low

(Shell/GUI)

Unix

Many Excellent High Many Expensive Excellent Servers

(Shell/GUI)

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

Introduction to Computing CS101

Next Lecture: Application SW

We'll learn about application SW, i.e. programs that interact directly with the user for the performance

of a certain type of work

We'll try to become familiar with various SW used in the following application areas:

Scientific/engineering/graphics

Business

Productivity

Entertainment

Educational

Table of Contents: