Master Boot Record (MBR) is a common type of hard disk. This post aims to introduce MBR and its partitions. What's more, you also can see the differences between MBR and GPT.

The hard disk boot record (MBR) does not belong to any operating systems. Therefore, it cannot be read by disk command. Fortunately, it can be read by INT13H provided by ROM-BIOS or DISKEDIT.DXE provided by Norton 8.0.

A master boot record consists of 4 parts including master boot program, error message data area, disk partition table, and end signature. The master boot program is responsible for loading and running the system. The partition table describes the partitions of a storage device and consist 4 partition entries, and each entry takes up 16 bytes space.

MBR and Hard Drive Partition

Hard disk is comprised of sectors and several sectors constitute a partition.

Note: All sectors in partition must be contiguous. And a MBR formatted hard disk supports up to four primary partitions or three primary partitions and an extended partition with up to 128 logical drives. 

If a hard disk has several primary partitions, users can install several different operating systems like Windows, Linux and Solaris on it.

Since MBR disk supports up to 4 primary partitions, the extended partition is widely used to meet users’ needs because an extended partition can be divided into multiple logical drives.

The boot record of logical drive is chained. Each logical partition has an extended boot record ( EBR ) which is similar to the MBR structure.

By default, Windows operating system will separate a primary partition to store system, and divide the remaining space into extended partition. 

Linux operating system will name the partition as sda1-sda4 or hda1-hda4. ( Note: the letter “a” represents the hard disk serial number ). For MBR disk, numbers 1-4 belong to primary partitions ( or extended partition ), and the serial number of logical partition starts from 5.)


MBR disk supports up to four primary partitions ( or three primary partitions and an extended partition ), and works with disk up to 2TB in size. GPT ( GUID Partition Table ) is a standard for the layout of the partition table on a physical hard disk. It can support hard disk over 2TB, and it allows users to create up to 128 partitions in Windows. Besides, the GPT partitioning scheme can improve the integrity of data structure since it provides backup-partition-table feature.

For more information about the difference between MBR and GPT, you can read this post:  MBR vs. GPT Guide: What’s The Difference and Which One Is BetterMBR and MBR partition

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