Editing Optical disc image

{{short description|Archive file of an optical disc}}
{{Multiple issues|
{{More citations needed|date=August 2011}}
{{Original research|date=November 2020}}
{{Essay-like|date=November 2020}}
}}
{{ infobox file format
| name          = ISO 9660 image
| mime          = application/vnd.efi.iso<ref>{{cite web |last1=Siyuan |first1=Fu |title=application/vnd.efi.iso |url=https://www.iana.org/assignments/media-types/application/vnd.efi.iso |publisher=[[IANA]] |access-date=18 July 2023 |date=24 January 2017}}</ref>
| magic         = [[ISO 9660#Volume descriptor|Volume descriptor]]: {{code|CD001}} at 32769. {{code|NSR0}} at 38913 or 32769 for UDF.<ref>{{cite web |title=File Signatures |url=https://www.garykessler.net/library/file_sigs.html |website=www.garykessler.net |access-date=2020-07-01 |archive-date=2020-07-03 |archive-url=https://web.archive.org/web/20200703084445/https://www.garykessler.net/library/file_sigs.html |url-status=live }}</ref>
| standard      = [[ISO 9660]], [[Universal Disk Format|UDF]]
| extensions    = .iso, .udf
| url           = 
| type code     = 
| uniform type  = public.iso-image
| owner         = 
| genre         = [[Disk image]]
| container for = 
| contained by  = 
| extended from = 
| extended to   = 
}}

An '''optical disc image''' (or '''ISO image''', from the [[ISO 9660]] file system used with [[CD-ROM]] media) is a [[disk image]] that contains everything that would be written to an [[optical disc]], [[disk sector]] by disc sector, including the optical disc [[file system]].<ref>{{cite web | url=https://www.lifewire.com/iso-file-2625923 | title=What Is an ISO File? | website=Lifewire | date=24 April 2018 | last=Fisher | first=Tim | access-date=23 June 2018 | archive-date=23 June 2018 | archive-url=https://web.archive.org/web/20180623113439/https://www.lifewire.com/iso-file-2625923 | url-status=live }}</ref> ISO images contain the binary image of an optical media [[file system]] (usually [[ISO 9660]] and its extensions or [[Universal Disk Format|UDF]]), including the data in its files in binary format, copied exactly as they were stored on the disc. The data inside the ISO image will be structured according to the file system that was used on the optical disc from which it was created.

ISO images can be created from optical discs by [[Comparison of disc image software|disk imaging software]], or from a collection of [[computer file|files]] by [[optical disc authoring software]], or from a different [[disk image#File formats|disk image file]] by means of [[data conversion|conversion]]. Software distributed on bootable discs is often available for download in ISO image format; like any other ISO image, it may be written to an optical disc such as CD, DVD and Blu-Ray.

== Description ==

Optical-disc images are uncompressed and do not use a particular container format; they are a [[disk sector|sector]]-by-sector copy of the data on an optical disc, stored inside a binary file. Other than ISO 9660 media, an ISO image might also contain a [[Universal Disk Format|UDF]] (ISO/IEC 13346) file system (commonly used by [[DVD]]s and [[Blu-ray Disc]]s), including the data in its files in binary format, copied exactly as they were stored on the disc. The data inside the ISO image will be structured according to the [[file system]] that was used on the optical disc from which it was created.

The ''.iso'' [[file extension]] is the one most commonly used for this type of disc images. The ''.img'' extension can also be found on some ISO image files, such as in some images from Microsoft [[DreamSpark]]; however, [[IMG (file format)|IMG files]], which also use the ''.img'' extension, tend to have slightly different contents. The ''.udf'' file extension is sometimes used to indicate that the file system inside the ISO image is actually UDF and not ISO 9660.

ISO files store only the user data from each sector on an optical disc, ignoring the [[CD-ROM#CD-ROM format|control headers]] and error correction data, and are therefore slightly smaller than a raw disc image of optical media. Since the size of the user-data portion of a sector (logical sector) in data optical discs is 2,048 bytes, the size of an ISO image will be a multiple of 2,048.

Any single-[[Track (CD)|track]] [[CD-ROM]], [[DVD]] or [[Blu-ray]] disc can be archived in ISO format as a true digital copy of the original. Unlike a physical optical disc, an image can be transferred over any data link or removable storage medium. An ISO image can be opened with almost every multi-format [[file archiver]]. Native support for handling ISO images varies from operating system to operating system.

With a suitable [[Device driver|driver]] software, an ISO can be "[[Mount (computing)|mounted]]" – allowing the operating system to interface with it, just as if the ISO were a physical optical disc. Most [[Unix]]-based operating systems, including [[Linux]] and [[macOS]], have this built-in capability to mount an ISO. Versions of Windows, beginning with [[Windows 8]], also have such a capability.<ref>{{Cite web |url=http://www.extremetech.com/computing/94370-windows-8-explorer-will-support-native-mounting-of-iso-and-vhd |title=Windows 8 Explorer will support native mounting of ISO and VHD |publisher=[[ExtremeTech]] |access-date=2012-05-21 |archive-date=2012-05-31 |archive-url=https://web.archive.org/web/20120531075941/http://www.extremetech.com/computing/94370-windows-8-explorer-will-support-native-mounting-of-iso-and-vhd |url-status=live }}</ref> For other operating systems, separately available software drivers can be installed to achieve the same objective.

== Multiple-track images ==

A CD can have multiple [[track (CD)|tracks]], which can contain computer data, audio, or video. [[File system]]s such as [[ISO 9660]] are stored inside one of these tracks. Since ISO images are expected to contain a binary copy of the file system and its contents, there is no concept of a "track" inside an ISO image, since a track is a container for the contents of an ISO image. This means that CDs with multiple tracks can not be stored inside a single ISO image; at most, an ISO image will contain the data inside one of those multiple tracks, and only if it is stored inside a standard file system.

This also means that [[Compact Disc Digital Audio|audio CD]]s, which are usually composed of multiple tracks, can not be stored inside an ISO image. Furthermore, not even a single track of an audio CD can be stored as an ISO image, since audio tracks do not contain a file system inside them, but only a continuous stream of encoded audio data. This audio is stored on [[Track (CD)#Subchannels|sectors of 2352 bytes]] different from those that store a file system and it is not stored inside files; it is addressed with ''track numbers'', ''index points'' and a ''CD time code'' that are encoded into the [[Lead-in (CD)|lead-in]] of each session of the CD-Audio disc.

[[Video CD]]s and [[Super Video CD]]s require at least two tracks on a CD, so it is also not possible to store an image of one of these discs inside an ISO image file, however an .IMG file can achieve this.

Formats such as [[Cue sheet (computing)|CUE/BIN]], [[CloneCD Control File|CCD/IMG]] and [[MDF and MDS file pair|MDS/MDF]] formats can be used to store multi-track disc images, including audio CDs. These formats store a raw disc image of the complete disc, including information from all tracks, along with a companion file describing the multiple tracks and the characteristics of each of those tracks. This would allow an optical media burning tool to have all the information required to correctly burn the image on a new disc. For audio CDs, one can also transfer the audio data into uncompressed audio files like [[WAV]] or [[Audio Interchange File Format|AIFF]], optionally reserving the metadata (see [[Ripping|CD ripping]]).

Most software that is capable of writing from ISO images to hard disks or recordable media (CD / DVD / BD) is generally not able to write from ISO disk images to [[USB flash drive|flash drive]]s. This limitation is more related to the availability of software tools able to perform this task, than to problems in the format itself. However, since 2011, various software has existed to write raw image files to USB flash drives.<ref>{{cite web | url=http://imagetousb.com/iso-image-to-usb-conversion/ | title=ISO image to USB conversion | publisher=ISO to USB burning tool | access-date=15 February 2015 | url-status=dead | archive-url=https://web.archive.org/web/20150215102916/http://imagetousb.com/iso-image-to-usb-conversion/ | archive-date=15 February 2015 }}</ref><ref>{{cite web | url=http://www.poweriso.com/tutorials/how-to-make-win7-bootable-usb-drive.htm | title=How to Setup Windows 7 or Windows 8 from USB drive? | publisher=PowerISO | access-date=15 February 2015 | archive-date=20 June 2016 | archive-url=https://web.archive.org/web/20160620222349/http://www.poweriso.com/tutorials/how-to-make-win7-bootable-usb-drive.htm | url-status=live }}</ref>

== Uses ==

.ISO files are commonly used in [[emulators]] to replicate a [[CD]] image. Emulators such as [[Dolphin (emulator)|Dolphin]] and [[PCSX2]] use .iso files to emulate [[Wii]] and [[GameCube]] games, and [[PlayStation 2]] games, respectively.<ref>{{cite web | url=https://dolphin-emu.org/docs/faq/#what-dump-formats-are-supported-dolphin | title=What dump formats are supported by Dolphin? | publisher=Dolphin Emulator Project | access-date=11 March 2021 | archive-date=4 March 2017 | archive-url=https://web.archive.org/web/20170304193029/https://dolphin-emu.org/docs/faq/#what-dump-formats-are-supported-dolphin | url-status=live }}</ref><ref>{{cite web | url=https://pcsx2.net/getting-started.html | title=So how do I use it? - PCSX2 | publisher=PCSX2 Team | access-date=11 March 2021 | archive-date=9 March 2021 | archive-url=https://web.archive.org/web/20210309011752/https://pcsx2.net/getting-started.html | url-status=live }}</ref> They can also be used as virtual CD-ROMs for hypervisors such as [[VMware Workstation]] or [[VirtualBox]]. Other uses are burning disk images of operating systems to physical install media.

== See also ==

* [[Comparison of disc image software]]
* [[Live USB]]
* [[No-disc crack]]

== References ==

{{refs}}

== External links ==

* [http://wiki.archlinux.org/index.php/Optical_disc_drive How to write ISO files to CD, DVD, and BD with Linux using genisoimage, wodim, growisofs, etc.]

{{Disk images}}

[[Category:Archive formats]]
[[Category:Disk images]]