A boot disk is a removable digital data storage medium from which a

computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...

can load and run (

boot A boot is a type of footwear. Most boots mainly cover the foot and the ankle, while some also cover some part of the lower calf. Some boots extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is cle ...

) 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. While almost all modern computers can boot from a hard drive containing the operating system and other software, they would not normally be called boot disks (because they are not removable media).

CD-ROM A CD-ROM (, compact disc read-only memory) is a type of read-only memory consisting of a pre-pressed optical compact disc that contains data. Computers can read—but not write or erase—CD-ROMs. Some CDs, called enhanced CDs, hold both comput ...

s are the most common forms of media used, but other media, such as magnetic or paper tape drives, ZIP drives, and more recently USB flash drives can be used. The computer's

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 ...

must support booting from the device in question. One can make one's own ''boot disk'' (typically done to prepare for when the system won't start properly).

Uses

Boot disks are used for: * Operating system installation * Data recovery *

Data purging Data remanence is the residual representation of digital data that remains even after attempts have been made to remove or erase the data. This residue may result from data being left intact by a nominal file deletion operation, by reformatting of ...

* Hardware or software troubleshooting *

BIOS flashing 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 b ...

* Customizing an operating environment * Software demonstration * Running a temporary operating environment, such as when using a Live USB drive. * Administrative access in case of lost password is possible with an appropriate boot disk with some operating systems * Games (e.g. for

Amiga Amiga is a family of personal computers introduced by Commodore in 1985. The original model is one of a number of mid-1980s computers with 16- or 32-bit processors, 256 KB or more of RAM, mouse-based GUIs, and significantly improved graphi ...

home computers, running MS-DOS video games on modern computers by using a bootable MS-DOS or FreeDOS USB flash drive).

Process

The term ''boot'' comes from the idea of lifting oneself by one's own bootstraps: the computer contains a tiny program (bootstrap loader) which will load and run a program found on a boot device. This program may itself be a small program designed to load a larger and more capable program, i.e., the full operating system. To enable booting without the requirement either for a mass storage device or to write to the boot medium, it is usual for the boot program to use some system RAM as a RAM disk for temporary file storage. As an example, any computer compatible with the

IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...

is able with built-in software to load the contents of the first 512 bytes of a floppy and to execute it if it is a viable program; boot floppies have a very simple loader program in these bytes. The process is vulnerable to abuse; data floppies could have a virus written to their first sector which silently infects the host computer if switched on with the disk in the drive.

Media

Bootable

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...

s ("boot floppies") for PCs usually contain DOS or miniature versions of Linux. The most commonly available floppy disk can hold only 1.4 MB of data in its standard format, making it impractical for loading large operating systems. The use of boot floppies is in decline, due to the availability of other higher-capacity options, such as

s or USB flash drives.

Device selection

A modern PC is configured to attempt to boot from various devices in a certain order. If a computer is not booting from the device desired, such as the floppy drive, the user may have to enter the BIOS Setup function by pressing a special key when the computer is first turned on (such as , , , or ), and then changing the boot order. More recent BIOSes permit the interruption of the final stage of the boot process and invoke the Boot Menu by pressing a function key (usually or ). This results in a list of bootable devices being presented, from which a selection may be made. Apple silicon Macs display the Boot Menu when the power button is pressed and held, the older Apple Macintosh computers with Intel processors will display the Boot Menu if user presses the or while the machine is starting.

Requirements

Different operating systems use different boot disk contents. All boot disks must be compatible with the computer they are designed for. ; MS-DOS/PC DOS/DR-DOS: *A valid boot sector in form of a volume boot record (VBR) *

IO.SYS is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS device drivers (hardware interfacing routines) and the DOS initialization program. Boot sequence In the PC bootup sequence, the first sector of the boot disk is ...

IBMBIO.COM IBMBIO.COM is a system file in many DOS operating systems. It contains the system initialization code and all built-in device drivers. It also loads the DOS kernel (IBMDOS.COM) and optional pre-loadable system components (like for disk compress ...

MSDOS.SYS MSDOS.SYS is a system file in MS-DOS and Windows 9x operating systems. In versions of MS-DOS from 1.1x through 6.22, the file comprises the MS-DOS kernel and is responsible for file access and program management. MSDOS.SYS is loaded by the DOS BI ...

IBMDOS.COM IBMDOS.COM is the filename of the DOS kernel. Loaded and initially invoked by the DOS BIOS in IBMBIO.COM during the boot process, it contains the hardware-independent parts of the operating system, including the embedded FAT12, FAT16 and ...

COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...

All files must be for the same version of the operating system. Complete boot disks can be prepared in one operation by an installed operating system; details vary. ; FreeDOS: *A valid boot sector on the disk *COMMAND.COM *KERNEL.SYS ; Linux: *A bootloader such as SYSLINUX or

GRUB Grub can refer to Grub (larva), of the beetle superfamily Scarabaeoidea, or as a slang term for food. It can also refer to: Places * Grub, Appenzell Ausserrhoden, Switzerland * Grub, St. Gallen, Switzerland * Grub (Amerang), a hamlet in Bavaria, ...

Linux kernel The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU ope ...

*Initial ram disk ( initrd) ; Windows Preinstallation Environment: *

Windows Boot Manager The booting process of Windows Vista and later versions differ from the startup process part of previous versions of Windows. In this article, unless otherwise specified, what is said about Windows Vista also applies to all later NT operatin ...

*BOOT.WIM

References

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External links

reboot.pro - Community forum dedicated to Boot Disks

Boot Disk information, sources, and tools
Bootable media