Operating System (CS2701)

Introduction to Operating System

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Dr. Rourab Paul

Computer Science Department, SNU University, Chennai

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Operating System

What OS?

An operating system is software that manages a computer’s hardware. It also provides a basis for application programs and acts as an intermediary between the computer user and the computer hardware.

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Room, timetable, teacher

• Teacher : Dr. Rourab Paul
• Computer Science Department
• Web: rourab.com

AI-DS-A:https://rourab.com/leclist.php?sub=OS&year=2025-2026&sec=AI-DS-A

AI-DS-B:https://rourab.com/leclist.php?sub=OS&year=2025-2026&sec=AI-DS-B

Cyber:https://rourab.com/leclist.php?sub=OS&year=2025-2026&sec=Cyber

• Email: rourabpaul@snuchennai.edu.in
• Skype: rourabpaul
• Room and Timetable
• Theory: Cyber 11:00 – 11:50 Monday, 308 AB3
• Theory: AIDS-A & AIDS-B 14:00 – 14:30 Monday, 304 AB3
• Theory: Cyber 08:10 – 09:00 Tuesday, 308 AB3
• Theory: AIDS-A & AIDS-B 08:10 – 09:00 Thursday, 304 AB3
• Theory: Cyber 09:00 – 09:50 Thursday, 308 AB3
• Theory: AIDS-A & AIDS-B 13:40 – 14:30 Friday, 304 AB3

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Evaluation Procedure

• Theory: 60 Marks:
• End Sem (Written): 30 marks
• Mid Sem (Written): 20 Marks
• CIA : 10 Marks

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• Lab: 40 Marks

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Story of Developing OS

1. The Early Days – No OS (1940s–1950s)

In the beginning, computers had no operating systems. Users programmed computers using machine code or punch cards, and each program had to include its own instructions to manage the hardware.

Problem: Every program had to talk directly to the hardware, which was inefficient and error-prone.

movie reco:

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Story of Developing OS

2. Batch Systems – The First OS (1950s–1960s) To improve efficiency, early OSs like IBM's GM-NAA I/O were created to automate job processing. These were called batch operating systems.

The OS would load one job, run it, and move to the next—no interaction during execution.

3. Interactive and Time-Sharing OS (1960s–1970s): The next leap came with time-sharing systems, allowing multiple users to interact with the computer simultaneously. OSs like MULTICS and later UNIX emerged.

Now multiple users could share a system, each getting a time slice of the CPU.

Unix – The Ancestor Born in 1969 at at: Bell Labs (AT&T) by Ken Thompson, Dennis Ritchie, Brian Kernighan, and others using C (a big deal for portability!)

4. The PC Era and Graphical OS (1980s–1990s)

As personal computers rose, OSs became user-friendly with GUIs (Graphical User Interfaces). Major players:

• MS-DOS, followed by Windows
• Mac OS from Apple
• Linux, an open-source UNIX-like OS started by Linus Torvalds in 1991

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“It's A UNIX System!" | Lex in Jurassic Park 1

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It’s one of the rare times a real operating system was shown accurately in a blockbuster

Building Blocks of OS

1. Bootloader

• The first code that runs when the computer powers on.
• Loads the OS kernel into memory.

2. Kernel

• Core part of the OS.
• Manages CPU, memory, I/O devices, and system calls.
• Types: Monolithic, Microkernel, Hybrid.

3. File System

• Organizes and manages storage devices.
• Provides folders, permissions, read/write operations.

4. Process Management: Handles running applications, CPU scheduling, process states.

5. Memory Management : Allocates RAM, handles paging/swapping.

6. Device Drivers :Interfaces between hardware and OS.

7. User Interface (Shell or GUI) : CLI (like Bash) or GUI (like GNOME, Windows Explorer).

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Computer-System Organization

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Storage Structure

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Thank You

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