UNIT 5 – OPERATING SYSTEMS (TEACHER EXPLANATION GUIDE)

🔷 5.1 WHAT IS AN OPERATING SYSTEM?

📘 Definition

An Operating System (OS) is system software that:
👉 Acts as an interface between user and hardware
👉 Manages all computer resources

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🎯 Simple Explanation for Students

“OS is like a manager of a computer.”

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🧠 Real-Life Analogy

• Computer = Restaurant
• OS = Manager
• CPU = Chef
• Users = Customers

👉 The manager (OS) decides:

• Who gets served first
• What resources to use

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🧩 Main Functions of OS

1. Process Management

Controls running programs

👉 Example:
Opening:

• Chrome
• Word
• Music player

OS decides which runs first

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2. Memory Management

Controls RAM usage

👉 Example:

• 4GB RAM
• Chrome uses 2GB
• Word uses 1GB

OS allocates memory properly

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3. File Management

Handles files & folders

👉 Example:
Saving a file in:

Documents > ICT > Notes.docx

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4. Device Management

Controls hardware

👉 Example:

• Printer
• Keyboard
• USB

Uses device drivers

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5. Security Management

Protects system

👉 Example:

• Password login
• Fingerprint

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🔷 Types of Operating Systems

1. Batch OS

• No interaction
  👉 Example:
  Payroll system

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2. Time-Sharing OS

• Multiple users at same time

👉 Example:
School computer lab

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3. Real-Time OS

• Immediate response

👉 Example:
Air traffic control

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4. Distributed OS

• Multiple computers act as one

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5. Embedded OS

• Inside devices

👉 Example:
Washing machine, ATM

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🔷 5.2 PROCESS MANAGEMENT

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📘 Definition

A process = a program in execution

👉 Example:

• Opening MS Word → becomes a process

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🧠 Process vs Program

Program	Process
Stored file	Running
Passive	Active

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🔄 Process States

1. New

Process is created

2. Ready

Waiting for CPU

3. Running

Currently executing

4. Waiting (Blocked)

Waiting for input

👉 Example:
Waiting for file to open

5. Terminated

Finished execution

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🎯 Teaching Analogy (VERY USEFUL)

👉 Students in a classroom:

• New → Student enters class
• Ready → Waiting for teacher
• Running → Answering question
• Waiting → Thinking / stuck
• Terminated → Finished

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🧮 CPU Scheduling

1. FCFS (First Come First Serve)

👉 Like queue in bank

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2. SJF (Shortest Job First)

👉 Short tasks first

Example:

• Print 1 page vs 100 pages

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3. Round Robin

👉 Each process gets equal time

👉 Like teacher giving each student chance

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🔄 Context Switching

Switching CPU between processes

👉 Example:
Switching between:

• Chrome → Word → YouTube

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🔷 5.3 MEMORY MANAGEMENT

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📘 Definition

Managing main memory (RAM) efficiently

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🧠 Key Concepts

Primary vs Secondary Memory

Primary	Secondary
RAM	Hard disk
Fast	Slow
Temporary	Permanent

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🔷 Memory Allocation

1. Fixed Partition

RAM divided into fixed blocks

👉 Problem: Wastage

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2. Dynamic Partition

Memory allocated as needed

👉 Better efficiency

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🔷 Paging

📘 Definition

Memory divided into:

• Pages (logical)
• Frames (physical)

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🧠 Simple Example

Think of:

• Book = program
• Pages = divided parts

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🔷 Virtual Memory

Using disk as extra RAM

👉 Example:
When RAM is full → uses hard disk

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🔷 Fragmentation

1. Internal Fragmentation

Unused space inside block

2. External Fragmentation

Free space scattered

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🔷 5.4 FILE MANAGEMENT

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📘 Definition

OS manages files and directories

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🧠 File Operations

• Create
• Read
• Write
• Delete

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📂 File Organization

1. Sequential Access

Read one by one

👉 Example:
Reading a book

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2. Direct Access

Jump to location

👉 Example:
Watching a specific video time

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📁 Directory Structure

👉 Example:

C:
 └── Users
      └── Student
           └── ICT
                └── Notes.txt

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🔷 5.5 DEVICE MANAGEMENT

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📘 Definition

Controls hardware devices

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🔌 Device Drivers

Software that connects OS to hardware

👉 Example:
Printer driver

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🔄 Interrupts

📘 Definition

Signal to CPU

👉 Example:

• Mouse click
• Keyboard press

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🧠 Simple Explanation

“Interrupt = asking CPU for attention”

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🔷 5.6 SECURITY & PROTECTION

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🔐 Authentication

Types:

• Password
• PIN
• Fingerprint
• Face ID

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🔑 Access Control

Who can access what

👉 Example:

• Admin vs Student

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🦠 Malware Types

1. Virus

Needs user action

👉 Example:
Opening infected file

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2. Worm

Spreads automatically

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3. Trojan

Looks safe but harmful

👉 Example:
Fake software