Unit 1: Introduction to Operating Systems (CS 4001/CB 4001/IT 4001)

For 4th Semester Polytechnic CS Students

Written by Garima Kanwar | Blog: Rajasthan Polytechnic

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📌 Introduction

Welcome to the Operating System (OS) Notes for 4th Semester Polytechnic CS Students. In this blog, we will cover detailed explanations with diagrams and symbols to help you understand OS concepts easily. Full PDF download and video lecture links are available below!

📢 🔔 Important:
👉 Full PDF available in our WhatsApp Group | Telegram Channel
👉 Watch the full lecture on YouTube: BTER Polytechnic Classes

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📌 1.1 Overview of Operating System

🖥️ What is an Operating System (OS)?

An Operating System (OS) is system software that acts as an interface between hardware and users. It manages system resources and allows users to run applications efficiently.

🔹 Examples of Operating Systems:
✔ Windows 🏠
✔ Linux 🐧
✔ macOS 🍏
✔ Android 🤖
✔ iOS 📱

🔄 Functions of an OS

1️⃣ Process Management – Controls running applications and assigns CPU time.
2️⃣ Memory Management – Allocates memory and prevents conflicts.
3️⃣ File System Management – Organizes and manages files/folders.
4️⃣ Device Management – Handles input/output devices.
5️⃣ Security & Access Control – Protects against unauthorized access.
6️⃣ User Interface (UI) – Provides CLI (Command Line) and GUI (Graphical User Interface).

📝 Diagram: OS as a bridge

👨‍💻 User ↔ OS ↔ Hardware 💾

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📌 1.2 Basic Concepts of OS

🔄 Process Management

A process is a program in execution. The OS ensures efficient execution of processes using: ✔ Multiprogramming – Runs multiple programs at once.
✔ Multitasking – Shares CPU time efficiently among processes.
✔ Threading – Runs smaller independent tasks inside a process.

💾 Memory Management

OS allocates and deallocates memory using:
✔ Paging (📑) – Divides memory into equal-sized blocks.
✔ Segmentation (📏) – Divides memory logically (Code, Stack, Data).
✔ Virtual Memory (💿) – Uses secondary storage as extra RAM.

📝 Diagram: Memory Allocation

+-----------------+
| Process 1 (👨‍💻) |
+-----------------+
| Process 2 (📂) |
+-----------------+
| Free Memory (💾) |
+-----------------+

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📌 1.3 UNIX/LINUX Architecture

UNIX/Linux OS follows a layered structure:

🔷 Components of UNIX/Linux Architecture

1️⃣ Shell (💻) – User interface for command execution.
2️⃣ System Call Interface (📞) – Connects applications to the kernel.
3️⃣ Kernel (🔧) – Controls hardware and system resources.
4️⃣ Hardware Layer (💾) – CPU, RAM, Hard Disk.

📝 Diagram: UNIX/Linux Architecture

+----------------------+
|   User Applications  |
+----------------------+
|       Shell (💻)       |
+----------------------+
| System Call Interface |
+----------------------+
|       Kernel (🔧)       |
+----------------------+
|      Hardware (💾)      |
+----------------------+

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📌 1.4 Kernel (🔧 Core of OS)

The Kernel is the heart of the OS. It directly communicates with hardware and manages system resources.

💡 Types of Kernels

✔ Monolithic Kernel (🧱) – All OS functions in one module (e.g., Linux).
✔ Microkernel (🔍) – Minimal kernel; runs services separately (e.g., Minix).
✔ Hybrid Kernel (⚡) – Combination of both (e.g., Windows NT).

📝 Diagram: Kernel in OS

+-----------------+
|   User Apps    |
+-----------------+
| System Calls  |
+-----------------+
|    Kernel (🔧)   |
+-----------------+
|    Hardware    |
+-----------------+

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📌 1.5 Services & System Calls

💡 OS Services

OS provides various services:
✔ File Management (📂) – Create, Read, Write, Delete files.
✔ Process Management (🔄) – Execute, suspend, terminate processes.
✔ Device Management (🖥️) – Controls hardware devices.
✔ Security (🔒) – Provides user authentication & access control.

📞 System Calls (Communication with OS)

System Calls allow programs to interact with the OS.

🔹 Examples of System Calls:
✔ Process Control – fork(), exec(), exit().
✔ File Management – open(), read(), write().
✔ Device Control – ioctl(), read(), write().

📝 Diagram: System Call Working

+-----------------+
| User Program (👨‍💻) |
+-----------------+
| System Call (📞) |
+-----------------+
|   OS Kernel (🔧)  |
+-----------------+
|   Hardware (💾)  |
+-----------------+

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📌 1.6 System Programs

🔹 What are System Programs?

System programs provide services to manage OS functions.

🖥️ Types of System Programs

✔ File Management (📂) – ls, cp, mv, rm.
✔ Process Management (🔄) – ps, kill, top.
✔ Device Management (🖥️) – mount, umount.
✔ Communication Programs (💬) – mail, write.

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🔚 Conclusion

📌 In this Unit 1 of Operating Systems (CS 4001/CB 4001/IT 4001), we learned: ✅ What is an OS & its functions 🖥️
✅ UNIX/Linux Architecture 🐧
✅ System Calls & Services 📞
✅ Kernel & System Programs 🔧

📢 🔔 Download PDF & Join Study Groups:
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📺 Watch Lecture on YouTube: BTER Polytechnic Classes
👉 📖 More Notes: Next Chapter – Process Management
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