Multiboot Specification

This file documents Multiboot Specification, the proposal for the boot sequence standard. This edition documents version 0.6.96. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions. This chapter describes some rough information on the Multiboot Specification. Note that this is not a part of the specification itself. Every operating system ever created tends to have its own boot loader. Installing a new operating system on a machine generally involves installing a whole new set of boot mechanisms, each with completely different install-time and boot-time user interfaces. Getting multiple operating systems to coexist reliably on one machine through typical chaining mechanisms can be a nightmare. There is little or no choice of boot loaders for a particular operating system — if the one that comes with the operating system doesn’t do exactly what you want, or doesn’t work on your machine, you’re screwed. While we may not be able to fix this problem in existing proprietary operating systems, it shouldn’t be too difficult for a few people in the free operating system communities to put their heads together and solve this problem for the popular free operating systems. That’s what this specification aims for. Basically, it specifies an interface between a boot loader and a operating system, such that any complying boot loader should be able to load any complying operating system. This specification does not specify how boot loaders should work — only how they must interface with the operating system being loaded. This specification is primarily targeted at PC, since they are the most common and have the largest variety of operating systems and boot loaders. However, to the extent that certain other architectures may need a boot specification and do not have one already, a variation of this specification, stripped of the x86-specific details, could be adopted for them as well. This specification is targeted toward free 32-bit operating systems that can be fairly easily modified to support the specification without going through lots of bureaucratic rigmarole. The particular free operating systems that this specification is being primarily designed for are Linux, the kernels of FreeBSD and NetBSD, Mach, and VSTa. It is hoped that other emerging free operating systems will adopt it from the start, and thus immediately be able to take advantage of existing boot loaders. It would be nice if proprietary operating system vendors eventually adopted this specification as well, but that’s probably a pipe dream. It should be possible to write compliant boot loaders that load the OS image from a variety of sources, including floppy disk, hard disk, and across a network. Disk-based boot loaders may use a variety of techniques to find the relevant OS image and boot module data on disk, such as by interpretation of specific file systems (e.g. the BSD/Mach boot loader), using precalculated blocklists (e.g. LILO), loading from a special boot partition (e.g. OS/2), or even loading from within another operating system (e.g. the VSTa boot code, which loads from DOS). Similarly, network-based boot loaders could use a variety of network hardware and protocols. It is hoped that boot loaders will be created that support multiple loading mechanisms, increasing their portability, robustness, and user-friendliness. It is often necessary for one reason or another for the user to be able to provide some configuration information to an operating system dynamically at boot time. While this specification should not dictate how this configuration information is obtained by the boot loader, it should provide a standard means for the boot loader to pass such information to the operating system. OS images should be easy to generate. Ideally, an OS image should simply be an ordinary 32-bit executable file in whatever file format the operating system normally uses. It