Editing Optical disc image (section)

== 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.