Editing Boot disk

{{short description|Removable disk from which a computer can boot an operating system}}
A '''boot disk''' is a removable [[Computer data storage|digital data storage medium]] from which a [[computer]] can load and run ([[booting|boot]]) an [[operating system]] or utility program.<ref name=RecovDSK.NYT98>{{cite news |newspaper=[[The New York Times]]
   |url=https://www.nytimes.com/1998/10/08/technology/q-a-emergency-preparedness.html
   |title=Emergency Preparedness
   |author=By J. D. Biersdorfer  |date=October 8, 1998}}</ref> 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]]s) that are bootable may be called ''boot drives''. [[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.

One can make one's own ''boot disk'' (typically done to prepare for when the system won't start properly).<ref>{{cite web
  |website=Hearst Newspapers
  |url=https://smallbusiness.chron.com/make-compaq-system-boot-disk-55875.html
  |title=How to Make a Compaq System Boot Disk}}</ref>

== Uses ==
Boot disks are used for:

* [[Operating system]] installation
* [[Data recovery]]
* [[Data purging]]
* Hardware or software troubleshooting
* [[BIOS flashing]]
* Customizing an operating environment
* Software demonstration<ref>{{cite magazine
   |magazine=[[PC World]]
   |url=https://www.pcworld.com/article/132086/article.html?page=11
   |title=How to Survive the Worst PC Disasters
   |quote=Download the demo and burn it to a bootable CD
   |date=May 23, 2007
   |page=11
   |access-date=August 23, 2020
   |archive-date=October 27, 2020
   |archive-url=https://web.archive.org/web/20201027175320/https://www.pcworld.com/article/132086/article.html?page=11
   |url-status=dead
   }}</ref>
* Running a temporary operating environment, such as when using a [[Live USB]] drive.<ref>{{cite news
      |newspaper=[[Computerworld]]
      |url=https://www.computerworld.com/article/2533304/can-i-recover-from-recovering-my-pc-.amp.html
      |title=Can I recover from recovering my PC?
      }}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
* Administrative access in case of lost password is possible with an appropriate boot disk with some operating systems
* Games (e.g. for [[Amiga games|Amiga]] 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 [[Bootstrapping|bootstrap]]s:<ref>a series of self-sustaining processes that proceed without external help: {{cite web
   |url=http://www.phrases.org.uk/meanings/290800.html
   |title='Pull yourself up by your bootstraps' - the meaning and origin of this phrase
   |first=Gary |last=Martin |website=Phrasefinder |accessdate=June 23, 2018}}</ref> 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 [[computer file|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 infects the host computer if switched on with the disk in the drive.

== Media ==
Bootable [[floppy disk]]s ("boot floppies") for PCs usually contain [[DOS]] or miniature versions of [[Linux]]. The most commonly available floppy disk can hold only 1.4 [[Megabyte|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]].

==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 {{Key|Delete}}, {{Key|F1}}, {{Key|F2}}, {{Key|F10}} or {{Key|F12}}), and then changing the boot order.<ref>{{cite magazine  |magazine=[[PC World]]
   |url=https://www.pcworld.com/article/241032/how-to-enter-your-pcs-bios.html
   |title=How to enter your PC's BIOS
   |quote= Need to change your computer's boot order or access other ..
   |date=October 5, 2011}}</ref> 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 {{Key|F11}} or {{Key|F12}}). 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 [[Mac (computer)|Mac]] computers with [[Intel]] processors will display the Boot Menu if user presses the {{key|Option}} or {{Key|Alt}} while the machine is starting.<ref>{{Cite web | url=https://support.apple.com/en-us/HT201255 | title=Mac startup key combinations }}</ref>

== 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]] 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;<ref name=RecovDSK.NYT98/> details vary.

; FreeDOS:
*A valid boot sector on the disk
*COMMAND.COM
*KERNEL.SYS

; Linux:
*A bootloader such as [[SYSLINUX]] or [[GRUB]]
*[[Linux kernel]]
*Initial ram disk ([[initrd]])

; Windows Preinstallation Environment:
*[[Windows Boot Manager]]
*BOOT.WIM

==See also==
* [[Data recovery]]
* [[El Torito (CD-ROM standard)]]
* [[Live CD]]
* [[Protected Area Run Time Interface Extension Services]] (PARTIES)
* [[Self-loader]]

==References==
{{reflist}}

== External links ==
* [http://reboot.pro/ reboot.pro - Community forum dedicated to Boot Disks]
* [http://bootdisk.com/ Boot Disk information, sources, and tools]

[[Category:Bootable media]]