Operating Systems: Comprehensive Overview

1. Introduction to Operating Systems

An Operating System (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. The OS acts as an intermediary between users and the computer hardware.

Purpose of an OS:

• Resource Management: Manages hardware resources like the CPU, memory, and storage.
• User Interface: Provides a user interface (UI) to interact with the computer.
• Application Management: Handles the execution of applications and services.
• File Management: Manages files and directories on storage devices.

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2. Types of Operating Systems

2.1. Batch Operating Systems

• Description: Executes batches of jobs with minimal user interaction.
• Example: Early mainframes.

2.2. Time-Sharing Operating Systems

• Description: Allows multiple users to share system resources simultaneously.
• Example: UNIX.

2.3. Multi-User and Multi-Tasking Operating Systems

• Description: Supports multiple users and tasks running concurrently.
• Example: Linux, Windows.

2.4. Real-Time Operating Systems (RTOS)

• Description: Provides immediate processing and response to events.
• Example: VxWorks, QNX.

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3. Key Components of an Operating System

3.1. Kernel

• Description: The core component of an OS responsible for managing hardware, system resources, and system calls.
• Function: Handles process management, memory management, device management, and system calls.
• Photo:
  Kernel Architecture

3.2. Process Management

• Description: Manages the execution of processes, including process scheduling and multitasking.
• Functions: Process creation, scheduling, termination.
• Photo:
  Process Management Diagram

3.3. Memory Management

• Description: Allocates and manages memory space for processes.
• Functions: Paging, segmentation, virtual memory.
• Photo:
  Memory Management Diagram

3.4. File System Management

• Description: Manages files and directories on storage devices.
• Functions: File creation, deletion, reading, writing.
• Photo:
  File System Diagram

3.5. Device Management

• Description: Manages hardware devices and peripherals.
• Functions: Device drivers, I/O operations.
• Photo: 
  Device Driver Overview

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4. Operating System Functions

4.1. Process Scheduling

• Description: Determines the order in which processes are executed.
• Algorithms: First-Come-First-Served (FCFS), Shortest Job First (SJF), Round Robin (RR).

4.2. Memory Allocation

• Description: Allocates memory space to processes.
• Techniques: Contiguous memory allocation, paging, segmentation.

4.3. File Operations

• Description: Provides operations for file manipulation.
• Operations: Open, read, write, close.

4.4. Input/Output Management

• Description: Manages input and output devices.
• Techniques: Buffering, spooling, device drivers.

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5. System Calls

5.1. Definition

• System calls are the interface between user applications and the OS kernel.

5.2. Examples

• Process Control: fork(), exec()
• File Management: open(), read(), write()
• Device Management: ioctl()

Photo: 
System Call Overview

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6. Security and Protection

6.1. Authentication

• Description: Ensures that users are who they claim to be.
• Methods: Passwords, biometrics.

6.2. Authorization

• Description: Grants users access to resources based on permissions.
• Methods: Access Control Lists (ACLs), Role-Based Access Control (RBAC).

6.3. Encryption

• Description: Protects data from unauthorized access.
• Types: Symmetric, asymmetric.