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

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

can load and run ( boot) an

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

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). Fixed drives (such as

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...

s) that are bootable may be called ''boot drives''.

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 computer data storage, data computers can read, but not write or erase. Some CDs, called enhanced CDs, hold b ...

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 drive A flash drive (also thumb drive, memory stick, and pen drive/pendrive) is a data storage device that includes flash memory with an integrated USB interface. A typical USB drive is removable, rewritable, and smaller than an optical disc, and u ...

s 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 a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

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

installation *

Data recovery In computing, data recovery is a process of retrieving deleted, inaccessible, lost, corrupted, damaged, overwritten or formatted data from computer data storage#Secondary storage, secondary storage, removable media or Computer file, files, when ...

* Data purging * Hardware or software troubleshooting * BIOS flashing * 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 produced by Commodore International, Commodore from 1985 until the company's bankruptcy in 1994, with production by others afterward. The original model is one of a number of mid-1980s computers with 16-b ...

home computers, running

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...

video games on modern computers by using a bootable

FreeDOS FreeDOS (formerly PD-DOS) is a free software operating system for IBM PC compatible computers. It intends to provide a complete MS-DOS-compatible environment for running Legacy system, legacy software and supporting embedded systems. FreeDOS ca ...

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 In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. In general, the term ''mass'' in ''mass storage'' is used to mean ''large'' in relation to contemporaneous hard disk drive ...

device or to write to the boot medium, it is usual for the boot program to use some system RAM as a

RAM disk A RAM drive (also called a RAM disk) is a block of random-access memory ( primary storage or volatile memory) that a computer's software is treating as if the memory were a disk drive (secondary storage). RAM drives provide high-performance te ...

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 List of IBM Personal Computer models, IBM PC model line and the basis for the IBM PC compatible ''de facto'' standard. Released on ...

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, a diskette, or a disk) is a 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 with a ...

s ("boot floppies") for PCs usually contain DOS or miniature versions of

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

. The most commonly available floppy disk can hold only 1.4 MB of data in its standard format, making it impractical for loading large

s. 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 Apple silicon is a series of system on a chip (SoC) and system in a package (SiP) processors designed by Apple Inc., mainly using the ARM architecture family, ARM architecture. They are used in nearly all of the company's devices including Mac ...

Macs display the Boot Menu when the power button is pressed and held, the older Mac computers with

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...

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 A boot sector is the disk sector, sector of a persistent data storage device (e.g., hard disk, floppy disk, optical disc, etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed by a computer system's bui ...

in form of a volume boot record (VBR) * IO.SYS or IBMBIO.COM * MSDOS.SYS or IBMDOS.COM * COMMAND.COM 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 *

Linux kernel The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...

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