Unit 1 – Computer Organisation

Operating System

Learning Objectives

After studying this topic, students will be able to:

• Understand the meaning of an Operating System.

• Explain the need for an Operating System.

• Identify the major functions of an Operating System.

• Understand different types of Operating Systems.

• Differentiate between various types of Operating Systems.

• Identify common Operating Systems used in computers and mobile devices.

Introduction to Operating System

An Operating System (OS) is system software that acts as an interface between the user and computer hardware.

It manages the computer's hardware and software resources and provides an environment in which application programs can run.

Simple Definition

An Operating System is system software that manages computer hardware and software resources and provides services to application programs and users.

Examples of Operating Systems include:

• Microsoft Windows

• Linux

• macOS

• Android

• iOS

• ChromeOS

Why Do We Need an Operating System?

A computer consists of many hardware components such as:

• CPU

• RAM

• Hard disk/SSD

• Keyboard

• Mouse

• Monitor

• Printer

• Network devices

Managing all these components directly would be very difficult for a normal user.

The Operating System provides a convenient way for users and applications to communicate with the hardware.

Examples of Operating Systems

Different Operating Systems are designed for different types of devices and requirements.

Main Objectives of an Operating System

The major objectives of an Operating System are:

1. Convenience – Make computers easier to use.

2. Resource Management – Manage CPU, memory, storage and I/O devices.

3. Efficiency – Use computer resources efficiently.

4. Security – Protect data and system resources.

5. Error Management – Detect and handle various system errors.

6. Program Execution – Provide an environment for programs to run.

Functions of an Operating System

An Operating System performs many important functions.

The major functions include:

1. Process Management

2. Memory Management

3. File Management

4. Device Management

5. User Interface

6. Security and Access Control

7. Resource Management

8. Error Detection and Handling

9. Storage Management

10. Networking

11. System Performance Monitoring

1. Process Management

A process is a program that is currently being executed.

The Operating System manages processes and decides how CPU time is allocated among them.

Example

Suppose a user is simultaneously:

• Playing music

• Browsing the Internet

• Editing a document

The Operating System manages the CPU and other resources required by these applications.

Functions of Process Management

• Creating processes

• Scheduling processes

• Allocating CPU time

• Managing process execution

• Terminating processes

• Coordinating processes

2. Memory Management

The Operating System manages the computer's main memory, particularly RAM.

It keeps track of:

• Which memory locations are being used.

• Which programs are using memory.

• How much memory is available.

• When memory should be allocated or released.

Example

When a user opens a web browser, the OS allocates RAM to the browser and its processes.

When the application is closed, the OS can reclaim that memory.

3. File Management

The Operating System manages files and folders stored on storage devices.

It allows users to:

• Create files

• Open files

• Rename files

• Copy files

• Move files

• Delete files

• Organise files into folders

• Control access to files

Example

When you create:

Class11_IT_Notes.pdf

the Operating System manages where and how the file is stored.

4. Device Management

The Operating System manages hardware devices connected to the computer.

Examples:

• Keyboard

• Mouse

• Printer

• Scanner

• Monitor

• Speakers

• USB devices

The OS communicates with many hardware devices using device drivers.

Example

When a printer is connected, the Operating System uses appropriate software/driver support to communicate with the printer.

5. User Interface

The Operating System provides an interface through which users interact with the computer.

Two major forms are:

Graphical User Interface (GUI)

Users interact using:

• Windows

• Icons

• Menus

• Buttons

• Pointers

Examples: Windows, macOS and many Linux desktop environments.

Command-Line Interface (CLI)

Users type commands to interact with the computer.

Example:

C:\> dir

or in a Unix/Linux shell:

$ ls

6. Security and Access Control

The Operating System helps protect the computer and its data.

Security functions may include:

• User accounts

• Passwords

• Permissions

• Access control

• Authentication

• Process isolation

• Security policies

Example

A school computer may have separate user accounts for:

• Administrator

• Teacher

• Student

Each account can be given different permissions.

7. Resource Management

A computer has limited resources such as:

• CPU time

• RAM

• Storage

• Network bandwidth

• Input/output devices

The Operating System manages these resources and allocates them to programs as required.

8. Error Detection and Handling

The Operating System monitors the computer system and helps detect and handle errors.

Examples:

• Application crashes

• Storage errors

• Invalid operations

• Device problems

• Memory-related problems

The OS may display an error message or take corrective action where possible.

9. Storage Management

The Operating System manages data stored on storage devices.

It keeps track of:

• Files

• Directories/folders

• Available storage space

• Storage allocation

• File permissions

• File systems

Examples of file systems include:

• NTFS

• FAT32

• exFAT

• ext4

• APFS

10. Networking

Modern Operating Systems provide networking capabilities.

They allow computers and applications to communicate over networks.

Networking functions include:

• Managing network connections

• Supporting network protocols

• Managing network devices

• Sharing resources

• Supporting Internet access
  

11. System Performance Monitoring

The Operating System can monitor system resources such as:

• CPU usage

• Memory usage

• Storage usage

• Network activity

• Running processes

For example, Task Manager in Windows allows users to view running processes and resource usage.

Types of Operating Systems

Operating Systems can be classified according to how they manage users, processes, tasks and resources.

Important types include:

1. Single-User Operating System

2. Multi-User Operating System

3. Single-Tasking Operating System

4. Multitasking Operating System

5. Batch Operating System

6. Multiprocessing Operating System

7. Multithreading Operating System

8. Real-Time Operating System

9. Distributed Operating System

10. Network Operating System

11. Embedded Operating System

12. Mobile Operating System

1. Single-User Operating System

A Single-User Operating System is designed primarily for one user at a time.

The system may still support multiple applications depending on the OS.

Example

Many personal computer operating systems are commonly used in a single-user setting.

2. Multi-User Operating System

A Multi-User Operating System allows multiple users to use computer resources, either simultaneously or through managed sessions.

The OS manages resources and access rights for different users.

Examples

• Linux/Unix server systems

• Windows Server

Uses

• Servers

• Universities

• Organisations

• Data centres

3. Single-Tasking Operating System

A Single-Tasking Operating System is designed to execute one main task at a time.

An early example is MS-DOS, which was primarily designed for command-line interaction and single-tasking use.

4. Multitasking Operating System

A Multitasking Operating System allows multiple processes or applications to make progress during the same period.

For example, a user can:

• Listen to music

• Browse the Internet

• Edit a document

at the same time.

Modern desktop and mobile Operating Systems support multitasking.

5. Batch Operating System

A Batch Operating System processes jobs in groups or batches without requiring continuous interaction from the user during processing.

Basic Working

Characteristics

• Jobs are collected.

• Similar jobs may be grouped.

• Jobs are processed automatically.

• User interaction during execution is limited.

Example Uses

Batch processing is useful for:

• Payroll processing

• Billing

• Large data processing

• Generating reports

6. Multiprocessing Operating System

A Multiprocessing Operating System supports systems with multiple processing units or CPU cores and can schedule work across them.

Modern computers commonly have processors with multiple cores.

Advantages

• Better performance

• Parallel execution

• Improved resource utilisation

• Better support for demanding workloads
  

7. Multithreading Operating System

A thread is a unit of execution within a process.

A multithreaded Operating System supports programs that contain multiple threads running concurrently.

Example

A web browser may use different threads for:

• User interface

• Network operations

• Page rendering

• Background tasks

Multithreading can improve responsiveness and resource utilisation.

8. Real-Time Operating System (RTOS)

A Real-Time Operating System is designed to respond to events within specified timing constraints.

The key feature is predictable response time.

RTOSs are commonly used where timing is critical.

Examples of Applications

• Industrial control systems

• Robotics

• Medical devices

• Automotive systems

• Aircraft systems

• Embedded controllers

Important Point

Real-time does not simply mean "very fast."

It means that the system is designed to provide responses within required timing constraints.

9. Distributed Operating System

A Distributed Operating System manages resources across multiple connected computers and can provide users with a unified system view.

The computers communicate and cooperate to perform tasks.

Concept

The resources of multiple computers can cooperate as part of a distributed system.

10. Network Operating System

A Network Operating System (NOS) is designed to provide and manage network-related services and resources.

It may provide:

• User management

• File sharing

• Printer sharing

• Network security

• Centralised resource management

Examples include server-oriented operating systems such as:

• Windows Server

• Linux server distributions

11. Embedded Operating System

An Embedded Operating System is designed for specialised devices with dedicated functions.

Examples include:

• Smart TVs

• Routers

• Printers

• Washing machines

• IoT devices

• Industrial controllers

• Automotive systems

Embedded systems generally have specific hardware and software requirements.

12. Mobile Operating System

A Mobile Operating System is designed specifically for mobile devices such as smartphones and tablets.

Major examples include:

Android

Developed around the Android platform and widely used on smartphones, tablets, TVs and other devices.

iOS

Apple's mobile operating system used on iPhone devices.

Mobile Operating Systems provide features such as:

• Touch interface

• Mobile networking

• App management

• Camera support

• Location services

• Power management

• Security
  

Graphical User Interface vs Command-Line Interface

Both interfaces can be useful depending on the task.

Comparison of Operating System Types

Difference Between Windows, Linux, macOS, Android and iOS

1. Windows

Windows is a family of Operating Systems developed by Microsoft.

It is widely used on personal computers.

Features

• Graphical user interface

• Multitasking

• Hardware and peripheral support

• Networking

• Security features

• Wide software compatibility

Common Uses

• Education

• Offices

• Programming

• Business

• Gaming

• Home computing

2. Linux

Linux is based on the Linux kernel and is widely used in servers, desktops, embedded systems and many other environments.

Popular Linux distributions include:

• Ubuntu

• Fedora

• Debian

• Linux Mint

Features

• Open-source ecosystem

• Highly configurable

• Strong server presence

• Powerful command-line tools

• Supports multiple users and multitasking

3. macOS

macOS is the Operating System developed by Apple for Mac computers.

Features

• Graphical interface

• Strong integration with Apple hardware

• Multitasking

• Security features

• Unix-based foundation

• Integration with other Apple services and devices
  

4. Android

Android is a mobile operating system platform based on the Linux kernel and maintained by Google with contributions from the broader Android ecosystem.

It is used on many smartphones and tablets.

Features

• Touch interface

• App ecosystem

• Notifications

• Mobile connectivity

• Location services

• Camera and multimedia support

5. iOS

iOS is Apple's mobile Operating System for iPhone.

Features

• Touch-based interface

• Strong hardware/software integration

• App ecosystem

• Security and privacy features

• Mobile networking

• Integration with Apple services

Operating System as a Resource Manager

One of the most important concepts is:

The Operating System acts as a resource manager.

It manages:

The OS decides how available resources are allocated among competing programs.

Operating System and Application Software

The Operating System and application software have different roles.

Operating System

Provides the platform and manages hardware resources.

Application Software

Performs specific tasks for the user.

Examples:

• Word processor

• Web browser

• Media player

• Image editor

• Spreadsheet software

Relationship

Booting

Booting is the process of starting a computer and loading the Operating System into memory.

Basic Boot Process

Firmware such as UEFI performs important early startup tasks before the OS is loaded.

Kernel

The kernel is the core component of an Operating System.

It manages important system resources and provides fundamental services to applications.

Major responsibilities include:

• CPU/process management

• Memory management

• Device management

• System calls

• Security and protection mechanisms

Simplified Structure

Device Drivers

A device driver is software that allows the Operating System to communicate with a particular hardware device.

For example:

The driver translates operating-system requests into operations the device can understand.

Summary of Operating System Functions

Important Differences

Single-Tasking vs Multitasking

Single-User vs Multi-User

Batch vs Real-Time

Windows vs Linux

Important Exam Questions

Very Short Answer Questions

Q1. What is an Operating System?

An Operating System is system software that manages computer hardware and software resources and provides services to application programs and users.

Q2. Give two examples of Operating Systems.

Windows and Linux.

Q3. What is the main purpose of an Operating System?

Its main purpose is to manage computer resources and provide an interface and environment for users and applications.

Q4. What is a kernel?

The kernel is the core component of an Operating System responsible for managing important hardware and system resources.

Q5. What is a device driver?

A device driver is software that enables an Operating System to communicate with a hardware device.

Q6. What is multitasking?

Multitasking is the ability of an Operating System to manage multiple processes so that they can make progress during the same period.

Q7. What is a real-time operating system?

An RTOS is an Operating System designed to provide responses within specified timing constraints.

Short Answer Questions

Q1. Why is an Operating System needed?

An Operating System is needed because it manages hardware resources, provides a user interface, manages files and memory, controls processes and allows application programs to use computer hardware.

Q2. Write any five functions of an Operating System.

Five important functions are:

1. Process management
   

2. Memory management
   

3. File management
   

4. Device management
   

5. Security and access control
   

Q3. What is the difference between GUI and CLI?

GUI allows users to interact with a computer through graphical elements such as windows, icons and menus. CLI allows users to interact by typing text commands.

Q4. What is the difference between batch and real-time operating systems?

A batch system processes jobs in groups with limited interaction during processing. A real-time system is designed to respond to events within specified timing constraints.

Long Answer Questions

Q1. Explain the major functions of an Operating System.

The major functions of an Operating System include process management, memory management, file management, device management, security, resource management, storage management, networking and providing a user interface.

It allocates CPU and memory resources, manages files and devices, controls running programs and provides a secure environment for users and applications.

Q2. Explain different types of Operating Systems.

Operating Systems can be classified into several types based on their method of operation and intended use. Important types include single-user, multi-user, single-tasking, multitasking, batch, multiprocessing, multithreading, real-time, distributed, network, embedded and mobile operating systems.

Each type is designed to meet different requirements. For example, batch systems are suitable for bulk processing, real-time systems are suitable for timing-sensitive applications, and mobile operating systems are designed for smartphones and tablets.

Multiple Choice Questions

1. Which software manages computer hardware and resources?

A. Application software

B. Operating System

C. Web browser

D. Word processor

Answer: B. Operating System

2. Which is an example of an Operating System?

A. MS Word

B. Photoshop

C. Linux

D. Chrome Browser

Answer: C. Linux

3. Which OS function manages RAM?

A. File management

B. Memory management

C. Printing

D. Networking

Answer: B. Memory management

4. Which type of OS is designed for timing-sensitive applications?

A. Batch OS

B. Real-Time OS

C. Single-user OS

D. Desktop OS

Answer: B. Real-Time OS

5. Which is a mobile Operating System?

A. Android

B. Windows Server

C. DOS

D. Ubuntu Server

Answer: A. Android

6. Which component is the core of an Operating System?

A. Browser

B. Kernel

C. Printer

D. Keyboard

Answer: B. Kernel

7. Which Operating System is developed by Apple for Mac computers?

A. Linux

B. Windows

C. macOS

D. Android

Answer: C. macOS

8. Which type of OS processes jobs in groups?

A. Real-Time OS

B. Batch OS

C. Mobile OS

D. Embedded OS

Answer: B. Batch OS

49. Fill in the Blanks

1. ________ is system software that manages computer resources.
   
   Answer: Operating System
   

2. The core of an Operating System is called the ________.
   
   Answer: Kernel
   

3. ________ manages the computer's main memory.
   
   Answer: Memory management
   

4. ________ manages files and folders.
   
   Answer: File management
   

5. ________ is a popular mobile Operating System.
   
   Answer: Android
   

6. ________ is Apple's Operating System for Mac computers.
   
   Answer: macOS
   

7. An OS designed to meet timing constraints is called a ________ Operating System.
   
   Answer: Real-Time
   

8. ________ allows users to interact with a computer using graphical elements.
   
   Answer: GUI
   

50. True or False

1. An Operating System manages computer hardware.
   
   True
   

2. Windows is an Operating System.
   
   True
   

3. RAM management is not the responsibility of an Operating System.
   
   False
   

4. Linux is based on the Linux kernel.
   
   True
   

5. Android is a mobile Operating System.
   
   True
   

6. A printer driver helps the OS communicate with a printer.
   
   True
   

7. A Real-Time OS simply means an OS that is always faster than other operating systems.
   
   False
   

8. An Operating System can manage multiple running processes.
   
   True
   

51. Quick Revision Sheet

Operating System

OS = Interface + Resource Manager + Service Provider

Main Functions

P – M – F – D – S

• P → Process Management
  

• M → Memory Management
  

• F → File Management
  

• D → Device Management
  

• S → Security
  

Other Important Functions

• Storage management
  

• Networking
  

• User interface
  

• Error handling
  

• Resource allocation
  

• Performance monitoring
  

Important Types

• Single-User
  

• Multi-User
  

• Single-Tasking
  

• Multitasking
  

• Batch
  

• Multiprocessing
  

• Multithreading
  

• Real-Time
  

• Distributed
  

• Network
  

• Embedded
  

• Mobile
  

Examples

Desktop: Windows, Linux, macOS

Mobile: Android, iOS

Server: Linux, Windows Server

Embedded: Special-purpose devices

Remember:

The Operating System is the manager of the computer's resources and the bridge between applications/users and hardware.