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An optical disc image (or ISO image, from the
ISO 9660 ISO 9660 (also known as ECMA-119) is a file system for optical disc media. Being sold by the International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard developm ...
file system used with
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—CD-ROMs. Some CDs, called enhanced ...
media) is a
disk image A disk image, in computing, is a computer file A computer file is a System resource, computer resource for recording Data (computing), data in a Computer data storage, computer storage device, primarily identified by its Filename, file name. ...
that contains everything that would be written to an
optical disc In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc that encodes binary data (bits) in the form of Compact disk#Physical details, pits and lands on a special material, often aluminum, ...
,
disk sector In computer disk storage, a sector is a subdivision of a Track (disk drive), track on a magnetic disk or optical disc. Each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs) and 2048 bytes ...
by disc sector, including the optical disc
file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage me ...
. ISO images are expected to contain the binary image of an optical media
file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage me ...
(usually
ISO 9660 ISO 9660 (also known as ECMA-119) is a file system for optical disc media. Being sold by the International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard developm ...
and its extensions or 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 disk imaging software, or from a collection of files by optical disc authoring software, or from a different disk image file by means of conversion. Software distributed on bootable discs is often available for download in ISO image format. And 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 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 UDF (ISO/IEC 13346) file system (commonly used by
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any k ...
s and
Blu-ray Disc The Blu-ray Disc (BD), often known simply as Blu-ray, is a Digital media, digital optical disc data storage format. It was invented and developed in 2005 and released on June 20, 2006 worldwide. It is designed to supersede the DVD format, and c ...
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 In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage me ...
that was used on the optical disc from which it was created. The ''.iso''
file extension A filename extension, file name extension or file extension is a suffix to the name A name is a term used for identification by an external observer. They can identify a class or category of things, or a single thing, either uniquely, or with ...
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 Microsoft Azure Dev Tools for Teaching or simply Azure Dev Tools for Teaching is a Microsoft program to provide students with Microsoft software design, Microsoft developer tools, Cloud Computing Access and learning resources. The program is a ...
; however, 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 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-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—CD-ROMs. Some CDs, called enhanced ...
,
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any k ...
or
Blu-ray The Blu-ray Disc (BD), often known simply as Blu-ray, is a Digital media, digital optical disc data storage format. It was invented and developed in 2005 and released on June 20, 2006 worldwide. It is designed to supersede the DVD format, and c ...
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. An ISO can be "mounted" with suitable driver software, i.e. treated by the operating system as if it were a physical optical disc. Most
Unix Unix (; trademarked as UNIX) is a family of Computer multitasking, multitasking, multiuser computer operating systems that derive from the original AT&T Corporation, AT&T Unix, whose development started in 1969 at the Bell Labs research center ...
-based operating systems, including
Linux Linux ( or ) is a family of free and open-source software, 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. Linu ...
and
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac (computer), Mac computers. Within the market of ...
, have built-in capability to mount an ISO. Versions of Windows beginning with
Windows 8 Windows 8 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on August 1, 2012; it was subsequently made available for downl ...
also have such capability. For other operating systems software drivers can be installed to achieve the same objective.


Multiple-track images

A CD can have multiple tracks, which can contain computer data, audio, or video.
File system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is Computer data storage, stored and retrieved. Without a file system, data placed in a storage me ...
s such as
ISO 9660 ISO 9660 (also known as ECMA-119) is a file system for optical disc media. Being sold by the International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard developm ...
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't 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
audio CD Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standardization, standard format for audio compact discs. The standard is defined in the ''Red Book'', one of a series of Rainbo ...
s, which are usually composed of multiple tracks, can't 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 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 of each session of the CD-Audio disc.
Video CD Video CD (abbreviated as VCD, and also known as Compact Disc Digital Video) is a home video format and the first format for distributing films on standard optical discs. The format was widely adopted in Southeast Asia, Central Asia and the ...
s and
Super Video CD Super Video CD (Super Video Compact Disc or SVCD) is a Digital data, digital format for storing video on standard compact discs. SVCD was intended as a successor to Video CD and an alternative to DVD-Video, and falls somewhere between both in ter ...
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/BIN, CCD/IMG and 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
AIFF Audio Interchange File Format (AIFF) is an audio file format standard used for storing sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human phy ...
, optionally reserving the metadata (see 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 flash drives. 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.


Uses

.ISO files are commonly used in emulators to replicate a CD image. Emulators such as
Dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the br ...
and PCSX2 use .iso files to emulate
Wii The Wii ( ) is a home video game console A home video game console is a video game console that is designed to be connected to a display device, such as a television, and an external power source as to play video games. Home consoles ...
and
GameCube The is a home video game console developed and released by Nintendo in Japan on September 14, 2001, in North America on November 18, 2001, and in PAL territories in 2002. It is the successor to the Nintendo 64 (1996), and predecessor of the Wii ...
games, and
PlayStation 2 The PlayStation 2 (PS2) is a home video game console developed and marketed by Sony Computer Entertainment. It was first released in Japan on 4 March 2000, in North America on 26 October 2000, in Europe on 24 November 2000, and in Australia on 3 ...
games, respectively. They can also be used as virtual CD-ROMs for hypervisors such as
VMware Workstation VMware Workstation Pro (known as VMware Workstation until release of VMware Workstation 12 in 2015) is a hosted (Type 2) hypervisor that runs on x64 versions of Windows and Linux operating systemshttps://kb.vmware.com/selfservice/microsites/searc ...
or
VirtualBox Oracle VM VirtualBox (formerly Sun VirtualBox, Sun xVM VirtualBox and Innotek VirtualBox) is a type-2 hypervisor for x86 virtualization developed by Oracle Corporation. VirtualBox was originally created by Innotek GmbH, which was acquired by S ...
. Other uses are burning disk images of operating systems to physical install media.


See also

*
Comparison of disc image software This article is a comparison of notable software applications that can access or manipulate disk image files. It compares their disk image handling features. Comparison criteria This article compares two features: Supported file formats and ca ...
* Live USB * No-disc crack


References


External links


How to write ISO files to CD, DVD, and BD with Linux using genisoimage, wodim, growisofs, etc.
{{Disk images Archive formats Disk images