📘 PAPER 5 – OPERATING SYSTEM (UNIT 1 – INTRODUCTION & PROCESS MANAGEMENT) university of allahabad

 

📘 PAPER 5 – OPERATING SYSTEM

🔴 UNIT 1 – INTRODUCTION & PROCESS MANAGEMENT

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1️⃣ Introduction to Operating System

✅ What is an Operating System (OS)?

An Operating System is system software that:

• Acts as an interface between user and hardware

• Manages computer resources

• Controls execution of programs

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✅ Functions of Operating System

✔ Process management
✔ Memory management
✔ File management
✔ Device management
✔ Security & protection
✔ User interface

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✅ Examples of Operating Systems

• Windows

• Linux

• macOS

• Android

• UNIX

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2️⃣ Types of Operating Systems

🔹 1. Batch Operating System

• Jobs executed in batches

• No user interaction

🔹 2. Multiprogramming OS

• Multiple programs in memory

• CPU utilization increases

🔹 3. Time Sharing OS

• Multiple users at same time

• CPU shared among users

🔹 4. Real-Time OS

• Immediate response

• Used in medical & industrial systems

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3️⃣ Structure of Operating System

🔹 Layered Structure

• Hardware at bottom

• User interface at top

• Easy to debug and maintain

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4️⃣ Process Concept

✅ Process

A process is a program in execution.

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Components of a Process

• Program counter

• Registers

• Stack

• Data section

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5️⃣ Process States

🔹 Five States of Process

State	Description
New	Process created
Ready	Waiting for CPU
Running	Executing
Waiting	Waiting for I/O
Terminated	Finished

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6️⃣ Process Control Block (PCB)

Definition:

PCB stores all information about a process.

Contains:

• Process ID

• Process state

• CPU registers

• Memory info

• Scheduling info

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7️⃣ Process Scheduling

Types of Scheduling:

1. Long-term scheduler

2. Short-term scheduler

3. Medium-term scheduler

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8️⃣ CPU Scheduling Algorithms

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🔹 1. FCFS (First Come First Serve)

✔ Simple
❌ High waiting time

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🔹 2. SJF (Shortest Job First)

✔ Minimum waiting time
❌ Starvation problem

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🔹 3. Priority Scheduling

• Process with highest priority executes first

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🔹 4. Round Robin

• Time quantum based

• Fair scheduling

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9️⃣ Process Synchronization

Problem:

When multiple processes access shared data → inconsistency occurs.

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🔹 Critical Section Problem

Requirements:

✔ Mutual Exclusion
✔ Progress
✔ Bounded Waiting

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🔟 Semaphores

Definition:

Semaphore is a synchronization tool.

Types:

1. Binary Semaphore

2. Counting Semaphore

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Operations:

wait()
signal()

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1️⃣1️⃣ Deadlock

Definition:

Deadlock occurs when:

• Each process waits for a resource held by others

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Conditions of Deadlock:

1. Mutual Exclusion

2. Hold and Wait

3. No Preemption

4. Circular Wait

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Deadlock Handling:

✔ Prevention
✔ Avoidance
✔ Detection
✔ Recovery

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1️⃣2️⃣ Inter-Process Communication (IPC)

Methods:

• Pipes

• Message Queues

• Shared Memory

• Signals

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📌 EXAM IMPORTANT QUESTIONS (UNIT 1)

✔ Explain process states
✔ Explain CPU scheduling algorithms
✔ Explain semaphore
✔ What is deadlock? Explain conditions
✔ Explain PCB
✔ Difference between process and program