Multiboot specification

Last updated

The Multiboot specification is an open standard describing how a boot loader can load an x86 operating system kernel. [1] [2] The specification allows any compliant boot-loader implementation to boot any compliant operating-system kernel. Thus, it allows different operating systems and boot loaders to work together and interoperate, without the need for operating system–specific boot loaders. As a result, it also allows easier coexistence of different operating systems on a single computer, which is also known as multi-booting.

Contents

The specification was originally created in 1995 and developed by the Free Software Foundation. GNU Hurd, VMware ESXi, Xen, and L4 microkernels all need to be booted using this method. GNU GRUB is the reference implementation used in the GNU operating system and other operating systems. [3]  As of July 2019, the latest version of Multiboot specification is 0.6.96, defined in 2009. [2] An incompatible second iteration with UEFI support, Multiboot2 specification, was later introduced. As of April 2019, the latest version of Multiboot2 is 2.0, defined in 2016. [4]

Technical overview [2] [4]

While Multiboot defines a header as a struct, which needs to be present in the image file as a whole, in Multiboot2, fields or group of fields have a type tag, which allows them to be omitted from the Multiboot2 header.

Within the OS image file, the header must be in the first 8192 (213) bytes for Multiboot and 32768 (215) bytes for Multiboot2. The loader searches for a magic number to find the header, which is 0x1BADB002 for Multiboot and 0xE85250D6 for Multiboot2.

In the header, entry_addr points to the code where control is handed over to the OS. This allows different executable file formats (see Comparison of executable file formats). If the OS kernel is an ELF file (Executable and Linkable Format), which it is for the Linux kernel, this can be omitted for Multiboot2. The ELF format is very common in the open source world and has its own field (e_entry) containing the entry point.

Before jumping to the OS entry point, the boot loader must provide a boot information structure to tell the OS how it left the system; for Multiboot, this is a struct, and for Multiboot2, every field (group) has a type tag and a size.

See also

Related Research Articles

<span class="mw-page-title-main">Executable and Linkable Format</span> Standard file format for executables, object code, shared libraries, and core dumps.

In computing, the Executable and Linkable Format, is a common standard file format for executable files, object code, shared libraries, and core dumps. First published in the specification for the application binary interface (ABI) of the Unix operating system version named System V Release 4 (SVR4), and later in the Tool Interface Standard, it was quickly accepted among different vendors of Unix systems. In 1999, it was chosen as the standard binary file format for Unix and Unix-like systems on x86 processors by the 86open project.

<span class="mw-page-title-main">ISO 9660</span> File system for CD-R and CD-ROM optical discs

ISO 9660 is a file system for optical disc media. The file system is an international standard available from the International Organization for Standardization (ISO). Since the specification is available for anybody to purchase, implementations have been written for many operating systems.

<span class="mw-page-title-main">Booting</span> Process of starting a computer

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 process must load software into memory before it can be executed. This may be done by hardware or firmware in the CPU, or by a separate processor in the computer system.

<span class="mw-page-title-main">Netwide Assembler</span> Assembler for the Intel x86 architecture

The Netwide Assembler (NASM) is an assembler and disassembler for the Intel x86 architecture. It can be used to write 16-bit, 32-bit (IA-32) and 64-bit (x86-64) programs. It is considered one of the most popular assemblers for Linux.

<span class="mw-page-title-main">Boot sector</span> Sector of a persistent data storage device

A boot sector is the sector of a persistent data storage device which contains machine code to be loaded into random-access memory (RAM) and then executed by a computer system's built-in firmware.

<span class="mw-page-title-main">Executable</span> A file that causes a computer to follow indicated instructions

In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instructions", as opposed to a

<span class="mw-page-title-main">Apple ProDOS</span> Operating system on Apple II series computers

ProDOS is the name of two similar operating systems for the Apple II series of personal computers. The original ProDOS, renamed ProDOS 8 in version 1.2, is the last official operating system usable by all 8-bit Apple II series computers, and was distributed from 1983 to 1993. The other, ProDOS 16, was a stop-gap solution for the 16-bit Apple IIGS that was replaced by GS/OS within two years.

<span class="mw-page-title-main">GNU GRUB</span> Boot loader package

GNU 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 user the choice to boot one of multiple operating systems installed on a computer or select a specific kernel configuration available on a particular operating system's partitions.

A boot disk is a removable digital data storage medium from which a computer can load and run (boot) an operating system or utility program. The computer must have a built-in program which will load and execute a program from a boot disk meeting certain standards.

<span class="mw-page-title-main">Multi-booting</span> Act of installing multiple operating systems on a single computer

Multi-booting is the act of installing multiple operating systems on a single computer, and being able to choose which one to boot. The term dual-booting refers to the common configuration of specifically two operating systems. Multi-booting may require a custom boot loader.

<span class="mw-page-title-main">Bootloader</span> Software responsible for starting the computer and load other software to the CPU memory

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.

<span class="mw-page-title-main">UEFI</span> Operating system and firmware specification

UEFI is a set of specifications written by the UEFI Forum. They define the architecture of the platform firmware used for booting and its interface for interaction with the operating system. Examples of firmware that implement these specifications are AMI Aptio, Phoenix SecureCore Tiano, TianoCore EDK II and InsydeH2O.

vmlinux Executable file containing the Linux kernel

vmlinux is a statically linked executable file that contains the Linux kernel in one of the object file formats supported by Linux, which includes Executable and Linkable Format (ELF) and Common Object File Format (COFF). The vmlinux file might be required for kernel debugging, symbol table generation or other operations, but must be made bootable before being used as an operating system kernel by adding a multiboot header, bootsector and setup routines.

<span class="mw-page-title-main">GUID Partition Table</span> Computer disk partitioning standard

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 identifiers (GUIDs). Forming a part of the Unified Extensible Firmware Interface (UEFI) standard, it is nevertheless also used for some BIOS systems, because of the limitations of master boot record (MBR) partition tables, which use 32 bits for logical block addressing (LBA) of traditional 512-byte disk sectors.

<span class="mw-page-title-main">EFI system partition</span> Partition used by Unified Extensible Firmware Interface

The EFIsystem partition or ESP is a partition on a data storage device that is used by computers having the Unified Extensible Firmware Interface (UEFI). When a computer is booted, UEFI firmware loads files stored on the ESP to start installing operating systems and various utilities.

<span class="mw-page-title-main">Fiwix</span> Operating system

Fiwix is an operating system kernel based on the UNIX architecture and fully focused on being POSIX compatible. It is designed and developed mainly as a hobbyist operating system, but it also serves for educational purposes. It runs on the i386 hardware platform and is compatible with a good base of existing GNU applications. It follows the System V Application Binary Interface and is also Linux 2.0 System Call ABI mostly compatible

The following tables compare general and technical information for a number of available bootloaders.

Hunk is the executable file format of tools and programs of the Amiga Operating System based on Motorola 68000 CPU and other processors of the same family. This kind of executable got its name from the fact that the software programmed on Amiga is divided in its internal structure into many pieces called hunks, in which every portion could contain either code or data.

The BIOS boot partition is a partition on a data storage device that GNU GRUB uses on legacy BIOS-based personal computers in order to boot an operating system, when the actual boot device contains a GUID Partition Table (GPT). Such a layout is sometimes referred to as BIOS/GPT boot.

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 MBRs was publicly introduced in 1983 with PC DOS 2.0.

References

  1. ↑ Merino Vidal, Julio M. (March 1, 2007), "Making NetBSD Multiboot-Compatible", ONLamp.com, O'Reilly Media , retrieved October 2, 2012.
  2. 1 2 3 Ford, Bryan; Boleyn, Erich Stefan; FSF (2009). "Multiboot specification" (0.6.96 ed.). GNU . Retrieved 2013-10-11.
  3. ↑ "Booting with GRUB". OSDEV. June 25, 2006. Archived from the original on December 28, 2008.
  4. 1 2 "Multiboot2 Specification version 2.0". www.gnu.org. Retrieved 7 April 2019.


This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.