An Operating System is the main software of a computer that controls all its activities and enables users to interact with the hardware.

Examples of Operating Systems

  • Microsoft Windows
  • Linux
  • macOS
  • Android
  • iOS

2. Purpose of an Operating System

The main purpose of an Operating System is to make the computer system convenient, efficient, and secure.

Objectives of an Operating System

  • Resource Management – Manages CPU, memory, storage, and I/O devices.
  • User Interface – Provides Graphical User Interface (GUI) or Command Line Interface (CLI).
  • Program Execution – Loads and executes application programs.
  • File Management – Organizes files and directories.
  • Memory Management – Allocates and deallocates memory.
  • Device Management – Controls peripheral devices like printers and keyboards.
  • Security – Protects the system from unauthorized access.
  • Error Handling – Detects and handles system errors.

3. Operating System Structure

The Operating System is organized into different layers that interact with users, applications, and hardware.

Structure Diagram

+-----------------------------+
|          Users              |
+-----------------------------+
             |
             v
+-----------------------------+
|    Application Programs     |
| (Browser, MS Word, Games)   |
+-----------------------------+
             |
             v
+-----------------------------+
|      Operating System       |
| • Process Management        |
| • Memory Management         |
| • File Management           |
| • Device Management         |
| • Security                  |
+-----------------------------+
             |
             v
+-----------------------------+
| Computer Hardware           |
| CPU, RAM, Disk, I/O Devices |
+-----------------------------+

Components of OS Structure

  1. Kernel – Core part of the operating system that manages hardware resources.
  2. Shell – Interface between the user and the kernel.
  3. File System – Manages files and directories.
  4. Device Drivers – Enable communication with hardware devices.
  5. System Libraries – Provide services to application programs.

4. Operating System Operations

An Operating System performs several important operations to manage system resources efficiently.

A. Process Management

  • Creates and terminates processes.
  • Schedules CPU time.
  • Supports multitasking.

B. Memory Management

  • Allocates memory to programs.
  • Frees memory after program execution.
  • Supports virtual memory.

C. File Management

  • Creates, deletes, and organizes files.
  • Controls file access permissions.

D. Device Management

  • Controls input/output devices.
  • Uses device drivers for communication.

E. Security Management

  • User authentication
  • Password protection
  • Access control

5. Dual-Mode Operation

Modern operating systems use Dual Mode to protect the computer system.

There are two execution modes:

1. User Mode

  • Used for application programs.
  • Has limited privileges.
  • Cannot directly access hardware.
  • Safer because it prevents accidental damage to the system.

2. Kernel Mode (Supervisor Mode)

  • Used by the operating system.
  • Has full access to hardware and memory.
  • Executes privileged instructions.

Diagram

+----------------------+
|      User Mode       |
| (Applications)       |
+----------+-----------+
           |
      System Call
           |
           v
+----------------------+
|     Kernel Mode      |
| (Operating System)   |
+----------------------+

Advantages of Dual Mode

  • Protects the operating system.
  • Prevents unauthorized hardware access.
  • Improves system security.
  • Enhances system stability.

6. Multi-Mode Operation

Some modern processors support multiple privilege levels instead of only two modes.

Example Privilege Levels

  • User Mode
  • Supervisor Mode
  • Hypervisor Mode (used in virtualization)
  • Machine/Firmware Mode

Advantages

  • Better security.
  • Fine-grained access control.
  • Supports virtualization technologies.
  • Efficient management of different system components.

7. Operating System as a Resource Manager

The Operating System acts as a Resource Manager because it controls and allocates all computer resources among multiple users and programs.

Resources Managed by the OS

ResourceFunction
CPUSchedules processes for execution
MemoryAllocates and frees RAM
StorageManages files and disks
Input/Output DevicesControls keyboards, printers, monitors, etc.
NetworkManages communication and data transfer

Responsibilities

  • Allocates resources efficiently.
  • Prevents resource conflicts.
  • Maximizes system performance.
  • Ensures fair resource sharing.
  • Protects resources from unauthorized access.

Resource Management Diagram

                Operating System
                       |
 -------------------------------------------------
 |         |          |          |               |
CPU      Memory      Files     Devices       Network
 |          |          |          |               |
Users and Application Programs Access Resources

Advantages of an Operating System

  • Easy interaction between users and hardware.
  • Efficient utilization of system resources.
  • Supports multitasking and multiprocessing.
  • Provides security and protection.
  • Improves system performance and reliability.
  • Simplifies application development.
Category: MCA

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