Disk Partitioning in Operating Systems 

1. What is Disk Partitioning (Real Meaning)

Disk partitioning divides a physical disk into logical sections, each acting like an independent disk.


Why This Exists

Without partitioning:

  • One disk → one big storage

  • No separation of OS, data, recovery


With Partitioning

Disk → Partition 1 (OS)  

     → Partition 2 (Data)  

     → Partition 3 (Backup)



Key Insight

Partition = logical division, not physical separation



2. Why Partitioning is Important


2.1 Isolation

  • OS crash doesn’t affect other partitions


2.2 Multi-OS Support

  • Install Linux + Windows


2.3 Better Organization

  • Separate system and user data


2.4 Performance & Management

  • Easier backup, recovery


3. Where Partition Info is Stored

Partition details are stored in:

Partition Table (at beginning of disk)

This table tells OS:

  • Where each partition starts

  • Where it ends

  • Type of file system


4. Two Major Partitioning Schemes


4.1 MBR (Master Boot Record)


What is MBR?

Old partitioning scheme stored in first sector of disk


Structure

  • Bootloader code

  • Partition table

  • Signature


Key Limitations

  • Max 4 primary partitions

  • Max disk size ≈ 2 TB


Visualization

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Extended Partition Concept

To bypass 4-partition limit:

  • 1 partition becomes extended

  • Inside it → multiple logical partitions


Key Insight

MBR uses workaround to extend partitions


4.2 GPT (GUID Partition Table)


What is GPT?

Modern partitioning system used with UEFI


Key Features

  • Supports 128+ partitions

  • Supports very large disks (ZB range)

  • Stores multiple partition tables (backup)


Visualization

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Key Insight

GPT = modern, scalable, reliable



5. MBR vs GPT (Important Comparison)

Feature

MBR

GPT

Max partitions

4 primary

128+

Disk size

~2 TB

Very large

Reliability

Low

High (backup table)

Boot system

BIOS

UEFI


6. Boot Process (Very Important Concept)

This is where partitioning becomes critical.


Step-by-Step Boot Flow


1. Power ON

  • CPU executes firmware


2. BIOS / UEFI Loads

  • BIOS (old) → MBR

  • UEFI (modern) → GPT


3. Bootloader Loaded

  • From disk


4. OS Kernel Loaded

  • OS starts


Key Insight

Partitioning determines how system boots



7. Boot Flow Visualization

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8. Real-World Example


Windows System

  • Uses NTFS

  • Uses GPT (modern systems)


Linux System

  • Uses ext4

  • Uses GPT