Master Boot Record - ArchWiki

# Master Boot Record

Related articles

- Arch boot process
- GUID Partition Table
- Partitioning
- Unified Extensible Firmware Interface

This article or section is a candidate for merging with Partitioning.

Notes: Keep info in one place (Discuss in Talk:Master Boot Record#Getting rid of "Master Boot Record" & "GUID Partition Table" articles)

The Master Boot Record (MBR) is the first 512 bytes of a storage device. It contains an operating system bootloader and the storage device's partition table. It plays an important role in the boot process under BIOS systems.

## Introduction

The MBR partition table stores the partitions info in the first sector of a hard disk as follows:

Location in the HDD | Purpose of the Code
--- | ---
`001-440 bytes` | MBR boot code that is launched by the BIOS.
`441-446 bytes` | MBR disk signature.
`447-510 bytes` | Partition table (of primary and extended partitions, not logical).
`511-512 bytes` | MBR boot signature 0xAA55.

The entire information about the primary partitions is limited to the 64 bytes allotted. To extend this, extended partitions were used. An extended partition is simply a primary partition in the MBR which acts like a container for other partitions called logical partitions. So one is limited to either 4 primary partitions, or 3 primary and 1 extended partitions with many logical partitions inside it.

### Problems with MBR

1. Only 4 primary partitions or 3 primary + 1 extended partitions (with arbitrary number of logical partitions within the extended partition) can be defined. If you have 3 primary + 1 extended partitions, and you have some free space outside the extended partition area, you cannot create a new partition over that free space.
2. Within the extended partition, the logical partitions' meta-data is stored in a linked-list structure. If one link is lost, all the logical partitions following that metadata are lost.
3. MBR supports only 1 byte partition type codes which leads to many collisions.
4. MBR stores partition sector information using 32-bit LBA values. This LBA length along with 512 byte sector size (more commonly used) limits the maximum addressable size of the disk to be 2 TiB. Any space beyond 2 TiB cannot be defined as a partition if MBR partitioning is used.

GUID Partition Table is the next generation partitioning scheme designed to succeed the Master Boot Record partitioning scheme method to fix above problems.

## Backup and restoration

See fdisk#Backup and restore and File recovery#Testdisk and PhotoRec.

## See also

- What is a Master Boot Record (MBR)?
- Understanding Disk Drive Terminology

Categories:

- Boot process
- Mainboards and BIOS
- System recovery

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