Boot disk
Encyclopedia
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.
Boot disks are used for:
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. Floppy disk
s and CD-ROM
s are the most common forms of media used, but other media, such as magnetic or paper tape drives, zip drive
s, and more recently USB flash drive
s can be used. The computer's BIOS
must support booting from the device in question.
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
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 infect the host computer if switched on with the disk in the drive.
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 system
s. The use of boot floppies is in decline, due to the availability of other higher-capacity options, such as CD-ROM
s or USB flash drives.
Modern Apple computers will boot from an appropriate disk if the user presses the C key while the machine is starting.
MS-DOS
All files must be for the same version; although MS-DOS 5 and 6 use a file called COMMAND.COM, they are not interchangeable. Complete boot disks can be prepared in one operation by an installed operating system; details vary.
Windows 8
Windows 8 has a feature called Windows To Go
, that allows the system to run from a USB flash drive, requiring only the extraction of files into the USB drive and the installation of a bootloader.
Linux
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
can load and run (boot
Booting
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
) an operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer 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.
Boot disks are used for:
- Operating system installation
- Data recoveryData recoveryData recovery is the process of salvaging data from damaged, failed, corrupted, or inaccessible secondary storage media when it cannot be accessed normally. Often the data are being salvaged from storage media such as internal or external hard disk drives, solid-state drives , USB flash drive,...
- Data purging
- Hardware or software troubleshooting
- Customizing an operating environment
- Software demonstration
- Administrative access in case of lost password is possible with an appropriate boot disk with some operating systems
- Games (e.g. for AmigaAmiga gamesAmiga games are computer games compatible with the Commodore Amiga.The Amiga was an important platform for games in the late 1980s and early 1990s. Of all the 16-bit home computers, it was the one to gain the greatest success as a games machine due to its graphic and sound subsystems, which were...
home computers)
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. Floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
s and CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
s are the most common forms of media used, but other media, such as magnetic or paper tape drives, zip drive
Zip drive
The Zip drive is a medium-capacity removable disk storage system that was introduced by Iomega in late 1994. Originally, Zip disks launched with capacities of 100 MB, but later versions increased this to first 250 MB and then 750 MB....
s, and more recently USB flash drive
USB flash drive
A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...
s can be used. The computer's BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
must support booting from the device in question.
The process of booting
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 storageMass storage
In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. Devices and/or systems that have been described as mass storage include tape libraries, RAID systems, hard disk drives, magnetic tape drives, optical disc drives, magneto-optical...
device or to write to the boot medium, it is usual for the boot program to use some system RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
as a RAM disk
RAM disk
A RAM disk or RAM drive is a block of RAM that a computer's software is treating as if the memory were a disk drive...
for temporary file
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
storage.
As an example, any computer compatible with the IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
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 infect the host computer if switched on with the disk in the drive.
Boot floppies
Bootable floppies for PCs usually contain MS-DOSMS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
or miniature versions of Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
. The most commonly available floppy disk can hold only 1.4 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
of data in its standard format, making it impractical for loading large operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s. The use of boot floppies is in decline, due to the availability of other higher-capacity options, such as CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
s or USB flash drives.
Booting from a disk
A modern PC is configured to attempt to boot from various devices in a certain order. If your computer is not booting from the device you desire, such as the floppy drive, you may have to enter the BIOS setup function by pressing a special key when the computer is first turned on -- Delete, F1, F2, F10 or F12 -- and then changing the boot order. More recent BIOSes permit the interruption of the final stage of the boot process by pressing a function key (usually F11). This results in a list of bootable devices being presented, from which a selection may be made.Modern Apple computers will boot from an appropriate disk if the user presses the C key while the machine is starting.
Required files
Different operating systems use different boot disk contents. All boot discs must be compatible with the computer they are designed for.MS-DOSMS-DOSMS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
/PC-DOSPC-DOSIBM PC DOS is a DOS system for the IBM Personal Computer and compatibles, manufactured and sold by IBM from the 1980s to the 2000s....
- A valid boot sectorBoot sectorA boot sector or boot block is a region of a hard disk, floppy disk, optical disc, or other data storage device that contains machine code to be loaded into random-access memory by a computer system's built-in firmware...
on the floppy disk, not in the format of a normal disk fileComputer fileA computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
. - IO.SYSIO.SYSIO.SYS is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS device drivers and the DOS initialization program.- Boot sequence :...
or IBMBIO.COMIBMBIO.COMIBMBIO.COM is the filename of the DOS-BIOS in many DOS operating systems, and as such part of PC-DOS, earlier versions of MS-DOS, and DR DOS 5.0 and higher... - MSDOS.SYSMSDOS.SYSMSDOS.SYS an important system file on MS-DOS and Windows 9x systems. It is run after IO.SYS. In MS-DOS, it contains the core operating system code, the kernel...
or IBMDOS.COMIBMDOS.COMIBMDOS.COM is the filename of the DOS kernel. It exists in DR-DOS and PC-DOS systems, with MS-DOS using MSDOS.SYS. The file is located in the root directory of the drive containing the operating system.... - COMMAND.COMCOMMAND.COMCOMMAND.COM is the filename of the default operating system shell for DOS operating systems and the default command line interpreter on Windows 95, Windows 98 and Windows Me...
All files must be for the same version; although MS-DOS 5 and 6 use a file called COMMAND.COM, they are not interchangeable. Complete boot disks can be prepared in one operation by an installed operating system; details vary.
Windows 8Windows 8Windows 8 is the codename for the next version of the Microsoft Windows computer operating system following Windows 7. It has many changes from previous versions. In particular it adds support for ARM microprocessors in addition to the previously supported x86 microprocessors from Intel and AMD...
Windows 8 has a feature called Windows To GoWindows To Go
Windows To Go is a feature in Windows 8 that allows the entire system to run from USB mass storage devices such as flash drives and external hard drives....
, that allows the system to run from a USB flash drive, requiring only the extraction of files into the USB drive and the installation of a bootloader.
LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
- A bootloader such as SYSLINUXSYSLINUXThe SYSLINUX Project is a suite of lightweight IBM PC MBR bootloaders for starting up computers with the Linux kernel. It is the work of H. Peter Anvin, and consists of several separate systems, the best-known of which is ISOLINUX.-List:...
or GRUB - Linux kernelLinux kernelThe Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
- Initial ram disk (initrd)
See also
- Live CDLive CDA live CD, live DVD, or live disc is a CD or DVD containing a bootable computer operating system. Live CDs are unique in that they have the ability to run a complete, modern operating system on a computer lacking mutable secondary storage, such as a hard disk drive...
- Boot sectorBoot sectorA boot sector or boot block is a region of a hard disk, floppy disk, optical disc, or other data storage device that contains machine code to be loaded into random-access memory by a computer system's built-in firmware...
- BootingBootingIn computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
- Windows To GoWindows To GoWindows To Go is a feature in Windows 8 that allows the entire system to run from USB mass storage devices such as flash drives and external hard drives....
- Darik's Boot and NukeDarik's Boot and NukeDarik's Boot and Nuke is an open source project hosted on SourceForge. The program is designed to securely erase a hard disk until data is permanently removed and no longer recoverable, which is achieved by overwriting the data with random numbers generated by Mersenne twister or ISAAC...
- Data recoveryData recoveryData recovery is the process of salvaging data from damaged, failed, corrupted, or inaccessible secondary storage media when it cannot be accessed normally. Often the data are being salvaged from storage media such as internal or external hard disk drives, solid-state drives , USB flash drive,...