Purpose of An Operating System (OS) (Copy)

Chapter 16.1: Purpose of an Operating System (OS)

1. Introduction to the Operating System

• An Operating System (OS) is the essential system software that manages hardware and software resources.
• It acts as an interface between users and computer hardware.
• The OS provides a user-friendly environment to execute applications and manage system resources efficiently.

2. Key Functions of an Operating System

1. Process Management
   • Manages execution of processes and applications.
   • Enables multitasking, allowing multiple processes to run simultaneously.
   • Uses scheduling algorithms to allocate CPU time effectively.
2. Memory Management
   • Allocates and deallocates memory dynamically as required by running processes.
   • Implements paging and segmentation to optimize memory utilization.
   • Manages virtual memory when RAM is insufficient.
3. File Management
   • Organizes and controls file storage.
   • Maintains a file system structure for efficient data access.
   • Provides security through access control mechanisms.
4. Device Management
   • Controls input/output devices using device drivers.
   • Allocates hardware resources to applications.
   • Manages interrupt handling to prioritize tasks.
5. User Interface
   • Offers Graphical User Interface (GUI) and Command-Line Interface (CLI).
   • Simplifies user interaction with system hardware.

3. Maximizing the Use of Computer Resources

• The OS ensures efficient utilization of system resources by managing:
  1. CPU Scheduling – Determines which process gets CPU time.
  2. Memory Optimization – Ensures memory is allocated properly.
  3. I/O System Management – Controls device communication.
• Direct Memory Access (DMA) Controller:
  • Allows hardware to access memory directly without CPU involvement.
  • Frees up CPU time for more critical tasks.
  • Ensures smooth I/O operations.

4. OS Boot Process

• The BIOS (Basic Input/Output System) initializes system hardware.
• A Bootstrap program loads the OS into RAM from storage.
• Tablets and mobile devices use flash memory for quick startup.
• The OS is split into:
  1. Read-only memory (OS files) – Cannot be modified by users.
  2. User-accessible memory (apps and data) – Used for running applications.

5. Kernel and Core OS Components

• The Kernel is the core of the OS, handling:
  • Process management
  • Memory management
  • Interrupt handling
  • Device management
  • File I/O operations
• Key Responsibilities of the Kernel:
  • Communicates between hardware and software.
  • Allocates CPU time and manages processes.
  • Handles interrupts to maintain system stability.

6. User Interaction and System Simplification

• The OS simplifies hardware complexity using:
  • Graphical User Interfaces (GUI)
  • Device drivers for managing hardware interaction.
  • File management tools for data access.
  • Background utilities, such as virus scanning and system updates.
• Example:
  • Older systems required manual command input for file transfers.
  • Modern OS allows drag-and-drop functionality to perform the same task.

7. Process Management and Scheduling

• Multitasking: Allows multiple processes to run simultaneously.
• Scheduling Algorithms:
  • Round Robin – Each process gets equal CPU time.
  • First Come First Serve (FCFS) – Executes tasks in order of arrival.
  • Shortest Job First (SJF) – Prioritizes shortest tasks.
  • Shortest Remaining Time First (SRTF) – Prioritizes tasks with least time left.
• Preemptive vs. Non-Preemptive Scheduling:
  • Preemptive: Allows process interruption for higher-priority tasks.
  • Non-Preemptive: A process must complete before switching.

8. Process States and Control

• A process can exist in different states:
  • Running: Executing on CPU.
  • Ready: Waiting for CPU time.
  • Blocked: Waiting for I/O operations.
• Process Control Block (PCB):
  • Stores information about each process, including:
    • Process ID
    • CPU registers
    • Memory allocations
    • Scheduling priority
• Context Switching:
  • Saves process state when switching between tasks.
  • Ensures processes resume from the last execution point.

9. Memory Management Techniques

• Paging: Divides memory into fixed-size blocks.
  • Uses a page table to map logical to physical addresses.
• Segmentation: Divides memory into variable-size blocks.
  • Reduces internal fragmentation but may lead to external fragmentation.
• Virtual Memory: Uses disk storage to extend available RAM.
  • Moves inactive processes to swap space to free up memory.
  • Disk thrashing occurs when excessive swapping reduces system performance.

10. Interrupt Handling and Priority Levels

• The OS prioritizes tasks based on Interrupt Priority Levels (IPL).
  • Example:
    • IPL 31: Power failure (highest priority).
    • IPL 24: System clock interrupts.
    • IPL 20-23: I/O device interrupts.
• Interrupt Handling Process:
  1. Interrupt is detected.
  2. The CPU stops the current process and saves its state.
  3. The OS looks up the Interrupt Dispatch Table (IDT).
  4. The required interrupt service routine (ISR) is executed.
  5. The previous process state is restored.

11. Security and System Protection

• The OS ensures data integrity, confidentiality, and security through:
  • Access control (user permissions)
  • Firewall and antivirus management
  • Data encryption
  • System updates and patches
  • Process isolation to prevent unauthorized access

12. Benefits of an Operating System

• Simplifies user interaction through GUI and automation.
• Optimizes resource management for better system performance.
• Enhances multitasking capabilities.
• Improves security by preventing unauthorized access.
• Facilitates software execution across different hardware platforms.