Master Boot Record (MBR) Explained

We use hard disks to store information and data. We create partitions on a hard disk to manage and store data efficiently. An MBR is a region on a hard disk that saves partition information.

MBR is a classic method to save partition information on a hard disk. It resides on the first sector of the boot disk. It stores disk partition information and a bootloader program. When we start a system, the BIOS scans all hard disks, detects the presence of MBR, loads the bootloader program in RAM from the default boot disk, executes the boot code to read the partition table, identifies the /boot partition, loads the kernel in RAM, and passes control over to it.

MBR supports three types of partition: primary, extended, and logical on a single disk. We can use only primary and logical partitions for data storage. We cannot use the extended partition for data storage. It stores logical partitions.

Technically, MBR supports only four primary partitions numbered from 1 to 4.

hard disk primary partitions

If we need more partitions, we need to convert the last primary partition into the extended partition. Inside the extended partition, we can create up to 11 logical partitions. Thus, we can create a maximum of 14 usable partitions (3 primary and 11 logical) on a single disk. The numbering for the logical partitions starts at 5.

hard disk extended paritions

Key points

  • MBR stores partition information and bootloader.
  • MBR uses the first sector of the hard disk to save the information.
  • Only BIOS-based systems use MBR.
  • UEFI-based systems do not use MBR. They use GPT to store partition information and bootloader programs.
  • MBR can store partition information for a hard disk of up to 2 TB.
  • MBR is non-redundant. It does not replicate the records it contains.
  • If MBR is corrupt, the system can't use it to boot.
  • MBR supports a maximum of 14 partitions.
  • We can create a maximum of 4 primary partitions. If we need more partitions, we need to convert the primary partition into an extended partition.
  • Within the extended partition, we can create a maximum of 11 logical partitions.

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