The BIOS boot partition is a partition on a

data storage device Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are cons ...

that

GNU GRUB GNU GRUB (short for GNU GRand Unified Bootloader, commonly referred to as GRUB) is a boot loader package from the GNU Project. GRUB is the reference implementation of the Free Software Foundation's Multiboot Specification, which provides a us ...

uses on legacy

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

-based

personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tech ...

s in order to boot an

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

, when the actual

boot device In computing, booting is the process of starting a computer as initiated via hardware such as a button or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some ...

contains a

GUID Partition Table The GUID Partition Table (GPT) is a standard for the layout of partition tables of a physical computer storage device, such as a hard disk drive or solid-state drive, using universally unique identifiers, which are also known as globally unique ...

(GPT). Such a layout is sometimes referred to as BIOS/GPT boot. A BIOS boot partition is needed on GPT-partitioned storage devices to hold the second stages of GRUB. On traditional

MBR MBR may refer to: Computing * Master boot record, the first sector of a partitioned data storage device, used for booting * Memory buffer register * Minimum bounding rectangle * Minimum bit rate Publications * ''The Malaysia Book of Records'' * ...

-partitioned devices, the

disk sector In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs) and 2048 bytes for CD-ROMs and ...

s immediately following the first are usually unused, as the partitioning scheme does not designate them for any special purpose and partitioning tools avoid them for alignment purposes. On GPT-based devices, the sectors hold the actual partition table, necessitating the use of an extra partition. On MBR-partitioned disks, boot loaders are usually implemented so the portion of their code stored within the MBR, which cannot hold more than 512 bytes, operates as a first stage that serves primarily to load a more sophisticated second stage, which is, for example, capable of reading and loading an

operating system kernel The kernel is a computer program at the core of a computer's operating system and generally has complete control over everything in the system. It is the portion of the operating system code that is always resident in memory and facilitates in ...

from a

file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one lar ...

Overview

When used, the BIOS boot partition contains the second stage of the

boot loader A bootloader, also spelled as boot loader or called boot manager and bootstrap loader, is a computer program that is responsible for booting a computer. When a computer is turned off, its softwareincluding operating systems, application code, an ...

program, such as the GRUB 2; the first stage is the code that is contained within the

Master Boot Record A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The concept of MB ...

(MBR). Use of this partition is not the only way BIOS-based boot can be performed while using GPT-partitioned hard drives; however, complex boot loaders such as GRUB 2 cannot fit entirely within the confines of the MBR's 398 to 446 bytes of space, thus they need an ancillary storage space. On MBR disks, such boot loaders typically use the sectors immediately following the MBR for this storage; that space is usually known as the "MBR gap". No equivalent unused space exists on GPT disks, and the BIOS boot partition is a way to officially allocate such space for use by the boot loader. The

globally unique identifier A universally unique identifier (UUID) is a 128-bit label used for information in computer systems. The term globally unique identifier (GUID) is also used. When generated according to the standard methods, UUIDs are, for practical purposes, un ...

(GUID) for the BIOS boot partition in the GPT scheme is (which, when written to a GPT in the required little endian fields, forms the ASCII string "Hah!IdontNeedEFI"). In the context of GPT on a BIOS-based computer, a BIOS boot partition is similar in some respects to the EFI system partition, which is used by systems based on EFI. The EFI System partition holds a filesystem and files used by the UEFI, while the BIOS boot partition is used in BIOS-based systems and accessed without a filesystem by holding raw binary code. The size requirements for a BIOS boot partition are quite low so it can be as small as about 30 KiB; however, as future boot loaders might require more space, 1 MiB might be a reasonable BIOS boot partition size. Due to the 1 MiB partition alignment policies used by most modern disk partitioning tools to provide optimum performance with

Advanced Format Advanced Format (AF) is any disk sector format used to store data on magnetic disks in hard disk drives (HDDs) that exceeds 512, 520, or 528 bytes per sector, such as the 4096, 4112, 4160, and 4224-byte (4 KB) sectors of an Advanced Format ...

disks, SSD devices and certain

RAID Raid, RAID or Raids may refer to: Attack * Raid (military), a sudden attack behind the enemy's lines without the intention of holding ground * Corporate raid, a type of hostile takeover in business * Panty raid, a prankish raid by male colleg ...

configurations, some room is left allowing the placement of a BIOS boot partition between the GPT and the first partition aligned that way. If created by utilizing that free space, the BIOS boot partition would be out of the GPT alignment specification, but that is not very important since it is written to very infrequently.

Creation

The following utilities are known to support BIOS boot partitions: *

cfdisk cfdisk is a Linux partition editor, similar to fdisk, but with a different, curses-based user interface. It is part of the util-linux package of Linux utility programs. The current cfdisk implementation utilizes the libfdisk library

fdisk In computing, the fdisk command-line utility provides disk-partitioning functions, preparatory to defining file systems. fdisk features in the DOS, DR FlexOS, IBM OS/2, and Microsoft Windows operating systems, and in certain ports of Free ...

GNU Parted GNU Parted (the name being the conjunction of the two words PARTition and EDitor) is a free partition editor, used for creating and deleting partitions. This is useful for creating space for new operating systems, reorganising hard disk usage, cop ...

(2.0 or later). *

GParted GParted (acronym of GNOME Partition Editor) is a GTK front-end to GNU Parted and an official GNOME partition-editing application (alongside Disks). GParted is used for creating, deleting, resizing, moving, checking, and copying disk partiti ...

, the front-end to GNU Parted. * gpt(8) partition editor in

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is a ...

(5.0 or later).
gdisk
GPT fdisk

References

{{Reflist

External links

BIOS installation
part of the GRUB2 documentation
The Funtoo Linux GUID Booting Guide

part of the GPT fdisk documentation

February 22, 2014, by Rod Smith BIOS Disk partitions

Overview

Creation

See also

References

External links