4. Components of Operating System

1. Two Main Components of OS

(A) User Space

What?

• Area where user applications run (e.g., GUI, CLI).

• Examples:

  • GUI (Graphical User Interface): Desktop icons, Windows Explorer.

  • CLI (Command Line Interface): Terminal (Linux), PowerShell (Windows).

Functions:

1. Provides convenient environment for users (e.g., drag-and-drop files).

2. Acts as a bridge between user and kernel (e.g., mkdir command → Kernel creates a folder).

Analogy:

• GUI/CLI = Restaurant menu (user interacts).

• Kernel = Kitchen (executes orders).

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(B) Kernel

What?

• Core of OS with direct hardware access.

• Functions:

  1. Process Management: Creates/schedules processes.

  2. Memory Management: Allocates/deallocates RAM.

  3. File Management: Manages files/folders (e.g., tree structure in Linux).

  4. I/O Management: Handles devices (USB, printer).

Key Term:

• Kernel Mode vs User Mode:

  • User Mode: Apps run with restricted access (e.g., mkdir command).

  • Kernel Mode: Full hardware access (e.g., creating the actual folder).

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2. How User Space and Kernel Work Together

Example: Creating a Folder

1. User Command: mkdir NewFolder (CLI) or Right-click → New Folder (GUI).

2. Kernel Action:

   • Switches to kernel mode.

   • File management allocates disk space.

   • Returns to user mode (confirmation message).

Visual Flow:

User Space (CLI/GUI) → Kernel (File Management) → Hardware (Disk)

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3. Types of Kernels

(A) Monolithic Kernel

What? All OS functions (process, memory, file, I/O) are inside the kernel.

• Examples: Linux, Unix, MS-DOS.

• Pros: Fast communication (all components in one place).

• Cons:

  • Bulky (large codebase).

  • Less reliable (if one component crashes, entire kernel fails).

(B) Microkernel

What? Only core functions (process/memory management) in kernel; rest (file/I/O) in user space.

• Examples: Symbian OS (old Nokia phones), MINIX.

• Pros:

  • Modular (easy to debug).

  • Reliable (file/I/O crashes don’t affect kernel).

• Cons:

  • Slower (frequent switches between user/kernel mode).

(C) Hybrid Kernel

What? Combines best of both (e.g., file management in user space, rest in kernel).

• Examples: Windows NT, macOS.

• Pros: Balanced speed and reliability.

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4. Key Concepts

(1) Inter-Process Communication (IPC)

Problem: How do processes in user space and kernel communicate?
Solutions:

1. Shared Memory: Processes read/write to a common memory area.

2. Message Passing: OS provides a channel (e.g., pipes in Linux).

(2) I/O Management Techniques

1. Buffering: Temporary storage (e.g., YouTube pre-loads video chunks).

2. Spooling: Queues tasks (e.g., printer jobs).

3. Caching: Stores frequently used data (e.g., browser cache).

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5. Interview Questions

1. Why is kernel called the "heart" of OS?

   • It manages all critical resources (CPU, RAM, devices).

2. What happens during a user-to-kernel mode switch?

   • Software interrupt triggers the switch (e.g., system calls like mkdir).

3. Which kernel type is used in modern OS?

   • Hybrid (e.g., Windows, macOS).

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6. Real-World Examples

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Key Takeaways:

1. User Space = Where apps run (GUI/CLI).

2. Kernel = Manages hardware (4 functions).

3. Kernel Types: Monolithic (fast but bulky), Micro (reliable but slow), Hybrid (best of both).