Day 1: **Introduction to Operating Systems**

Date: January 13, 2025

Operating Systems (OS) are the backbone of computing, bridging the gap between hardware and user-level applications. Whether you're a student diving into computer science or a professional aiming to ace interviews, a solid understanding of OS fundamentals is essential. Let's explore Day 1 of our 5-day learning journey.

---

Goals for the Day

1. Understand the basics of operating systems.
2. Learn about the structure, types, and functionality of an OS.

---

What is an Operating System?

Definition and Importance

An Operating System (OS) is system software that manages computer hardware and software resources while providing services for application programs. Essentially, it acts as an intermediary between the user and the computer hardware.

• Why is the OS important?
  • It simplifies interaction with the hardware.
  • Ensures optimal utilization of resources.
  • Provides security, efficiency, and convenience for users and applications.

Examples of Operating Systems

• Desktop OS: Windows, macOS, Linux.
• Mobile OS: Android, iOS.
• Server OS: Windows Server, Unix, Red Hat Enterprise Linux.

---

Types of Operating Systems

1. Batch Operating System

• Tasks are collected in batches, and the OS executes them one after another.
• Example: Early IBM systems.
• Limitation: No user interaction during execution.

2. Time-Sharing Operating System

• Allows multiple users to share system resources simultaneously.
• Provides a quick response by allocating CPU time to tasks in small time slices.
• Example: Unix.

3. Distributed Operating System

• Resources are distributed across multiple systems, appearing as a single coherent system.
• Example: Amoeba, Windows Server 2019.

4. Real-Time Operating System (RTOS)

• Ensures that tasks are executed within strict time constraints.
• Used in embedded systems like medical devices and automotive systems.
• Example: VxWorks, FreeRTOS.

5. Mobile Operating System

• Designed for smartphones and tablets with specialized features like touch interfaces.
• Example: Android, iOS.

---

Functions of an Operating System

1. Process Management

• Manages processes, including their creation, scheduling, and termination.
• Ensures smooth execution of multiple programs.

2. Memory Management

• Allocates and deallocates memory to applications.
• Ensures efficient use of RAM and prevents memory leaks.

3. File System Management

• Organizes, stores, and retrieves data on storage devices.
• Provides access control for files and directories.

4. Device Management

• Handles communication between the system and hardware devices.
• Manages drivers for peripherals like printers and storage.

---

System Calls

Introduction

System calls are the interface between user applications and the OS. They allow applications to request services such as file access, process creation, and network communication.

Examples of System Calls

1. Process Control: fork(), exec()
2. File Management: open(), read(), write(), close()
3. Device Management: ioctl(), read(), write()
4. Information Maintenance: getpid(), alarm()
5. Communication: pipe(), send(), recv()

---

Activities

1. Read/Watch

• Study foundational OS topics from textbooks like Operating System Concepts by Silberschatz.
• Watch introductory videos on YouTube (e.g., "What is an Operating System?" by FreeCodeCamp or Computerphile).

2. Hands-On Practice

If you have access to a Linux system:

• Commands to try:
  • ls: List files and directories.
  • cd: Change directories.
  • ps: Display current processes.
  • top: Monitor system resource usage.
• Objective: Familiarize yourself with how the OS interacts with files, directories, and processes.

---

Interview Preparation

Common Questions

1. What is an operating system?

   • It is software that manages hardware and software resources while providing an interface for user applications.

2. Explain the different types of operating systems.

   • Batch, time-sharing, distributed, real-time, and mobile OS, each designed for specific use cases.

3. What are system calls? Provide examples.

   • System calls are the interface between user applications and the OS, such as fork() for process creation or read() for file input.

---

Outcome

By the end of Day 1, you should:

• Have a clear understanding of what an OS is and its importance.
• Be familiar with the types and functions of operating systems.
• Understand the role of system calls and how they enable application-OS interaction.

---

This foundational knowledge will prepare you for deeper concepts like process management, which we'll explore on Day 2. If you'd like more detailed explanations or help with examples, let me know!