# optical disc image

> archive file of an optical disc

**Wikidata**: [Q877050](https://www.wikidata.org/wiki/Q877050)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Optical_disc_image)  
**Source**: https://4ort.xyz/entity/optical-disc-image

## Summary
An optical disc image is an archive file that stores the complete contents and structure of an optical disc volume. It functions as a specific type of disk image, designed to replicate the data from optical media such as CDs, DVDs, or Blu-rays. This format enables the exact duplication and backup of disc data for storage or distribution.

## Key Facts
- Defined as an archive file of an optical disc and classified as an instance of a disk image.
- Commonly identified by the file extensions .iso and .img.
- Associated with the media types `application/x-iso9660-image` and `application/vnd.efi.iso`.
- Recognized by the hexadecimal file format identification pattern `426C696E6B20627920442E542E53`.
- Registered in PRONOM with the format ID `fmt/468` and in the Library of Congress as `fdd000348`.
- Holds a Freebase ID of `/m/01yr3k` and a Niconicopedia ID of `iso`.
- Functions as a subclass of both "disk image" and "filename extension".
- Distinct from the entity "ISO" according to specific references.
- The Wikipedia entry is titled "Optical disc image" and includes 28 sitelinks across 28 languages.
- Associated topics include "ISO-Image" on Quora and "iso-files" on GitHub.
- Related to "Delta ISO," a mechanism used to update ISO images.

## FAQs
**What file extensions are associated with an optical disc image?**
Optical disc images typically utilize the file extensions .iso and .img.

**How is this format classified within file system hierarchies?**
It is classified as a subclass of both "disk image" and "filename extension," serving as a specific instance of a disk image intended for optical discs.

**What are the official media types assigned to this format?**
The format is associated with the media types `application/x-iso9660-image` and `application/vnd.efi.iso`.

**Is an optical disc image the same thing as an ISO?**
While closely related, the optical disc image is explicitly defined as different from the entity "ISO" in specific data references, though the terms are often used interchangeably in general contexts.

**How is the file format identified technically?**
The format can be identified by the hexadecimal pattern `426C696E6B20627920442E542E53` and is described using a 010 Editor Binary Template.

## Why It Matters
Optical disc images are essential for digital preservation and software distribution because they create a perfect bit-for-bit copy of physical media. By archiving the contents and structure of a disc volume, they solve the problem of physical media degradation and allow for the efficient duplication of data without requiring the physical disc. The format's integration with update mechanisms like Delta ISO further enhances its utility, enabling users to patch large software images without re-downloading the entire file.

## Notable For
- Being documented across 28 different language versions of Wikipedia.
- Possessing a specific hexadecimal identification pattern (`426C696E6B20627920442E542E53`) used for technical file recognition.
- Having a dedicated update mechanism known as Delta ISO, which serves as a related class.
- Being recognized by major archival standards bodies such as PRONOM and the Library of Congress.
- Supporting a wide array of international aliases, including "ISO-Speicherabbild," "ISO映像檔," and "ISO образ."

## Body

### Definition and Classification
An optical disc image is fundamentally an archive file that replicates the contents and structure of an optical disc. It is categorized specifically as an instance of a "disk image," which is a broader class of computer files containing the contents and structure of a disk volume. Within the hierarchy of data types, the optical disc image acts as a subclass of both "disk image" and "filename extension." It is distinct from the entity "ISO," despite the frequent overlap in nomenclature.

### Technical Specifications and Identification
The format is technically identified by a specific hexadecimal pattern: `426C696E6B20627920442E542E53`. This pattern is located at offset 0 and is used to verify the file type. The structure of the optical disc image is detailed in resources such as the 010 Editor Binary Template, available at a specific URL describing the ISO format.

### File Extensions and Media Types
Optical disc images are most commonly associated with the file extensions .iso and .img. The format supports various media types registered for digital interchange:
*   `application/x-iso9660-image`: Referenced by Apache HTTPD documentation and freedesktop.org shared-mime-info.
*   `application/vnd.efi.iso`: Referenced by the Internet Assigned Numbers Authority (IANA).

### Aliases and Global Terminology
The entity is known by a multitude of aliases across different languages and regions, reflecting its global adoption. These include:
*   **English:** ISO image, ISO-Image
*   **German:** ISO-Speicherabbild, ISO-Datei, ISO-Image, ISO-Dateiformat
*   **Spanish:** Imágenes ISO, Imagenes ISO
*   **Japanese:** ISO映像檔
*   **Russian:** ISO образ
*   **General:** .iso, .img, ISO

### Archival and Documentation
Several major organizations have standardized the identification of this format:
*   **PRONOM:** Assigned the file format ID `fmt/468`.
*   **Library of Congress:** Listed under the format description document ID `fdd000348`.
*   **Freebase:** Categorized under the ID `/m/01yr3k`.
*   **Niconicopedia:** Indexed with the ID `iso`.

### Ecosystem and Related Entities
The optical disc image exists within a broader ecosystem of related technologies and classes:
*   **Delta ISO:** This is a related class defined as a mechanism to update ISO images, allowing for efficient modifications to the base image file.
*   **Disk Image:** The parent class that encompasses optical disc images as well as other volume structures.
*   **Community Topics:** The format is the subject of specific topics on platforms like Quora ("ISO-Image") and GitHub ("iso-files").

### Wikipedia Presence
The concept is extensively documented on Wikipedia under the title "Optical disc image." The entry boasts a significant presence with 28 sitelinks, indicating translations and articles in 28 languages, including Arabic, German, English, Spanish, French, Japanese, Korean, Russian, Chinese, and others. This wide linguistic coverage underscores the format's universal relevance in computing.

## References

1. Freebase Data Dumps. 2013
2. [Source](https://svn.apache.org/repos/asf/httpd/httpd/tags/2.4.34/docs/conf/mime.types)
3. [Source](https://gitlab.freedesktop.org/xdg/shared-mime-info/-/commit/7fd0d942bf0a541b60b1bbf638ffff4b4f838e4d)
4. [Source](https://www.iana.org/assignments/media-types/application/vnd.efi.iso)
5. Quora
6. Gary Kessler's File Signature Table