# optical disc

> flat and usually circular disc which encodes binary data, primarily used for physical data distribution and long-term archival

**Wikidata**: [Q234870](https://www.wikidata.org/wiki/Q234870)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Optical_disc)  
**Source**: https://4ort.xyz/entity/optical-disc

## Summary  
An optical disc is a flat, usually circular, removable medium that stores binary data using laser‑readable pits and lands. It is the primary physical format for distributing software, music, movies, and for long‑term archival storage.

## Key Facts  
- **Physical form**: Disk‑shaped, most commonly 120 mm in diameter; a 80 mm “mini” version also exists.  
- **Data encoding**: Binary data is encoded as microscopic pits and lands read by an optical disc drive.  
- **Classification**: Subclass of optical storage, machine‑readable medium, computer storage media, and removable media.  
- **First commercial formats**: LaserDisc (1978) and Compact Disc (CD, 1979) introduced consumer‑grade optical discs.  
- **Major families**: Includes CD, DVD, Blu‑ray Disc (2006), M‑Disc, Archival Disc (2016), and many specialized variants (e.g., MP3 CD, CD+G, Ultra HD Blu‑ray).  
- **Long‑term archival**: Formats such as M‑Disc and Archival Disc are designed for multi‑decadal data preservation.  
- **Usage**: Read and written by optical disc drives found in computers, game consoles, and dedicated players.  
- **Unicode symbols**: Represented by 💿 and 🖸.  
- **Aliases**: Also known as optical media, optical disk, disque laser, optische Platte, among others.  

## FAQs  
### Q: What is an optical disc?  
A: It is a removable, flat circular medium that stores digital information as microscopic pits read by a laser, enabling data distribution and archival.  

### Q: How does an optical disc differ from a magnetic hard drive?  
A: Optical discs use light to read/write data and are typically removable, whereas magnetic drives use magnetic fields on non‑removable platters and require electrical heads for access.  

### Q: What sizes do optical discs come in?  
A: The standard size is 120 mm (≈ 4.7 in) in diameter; a smaller 80 mm (≈ 3.1 in) “mini” version is also common for portable devices.  

## Why It Matters  
Optical discs revolutionized how media and software are distributed, offering a low‑cost, durable, and portable solution that does not require power to retain data. Their removable nature made them ideal for consumer products such as music CDs, DVDs, and video games, while specialized formats like M‑Disc and Archival Disc provide reliable long‑term storage for libraries, archives, and enterprises. Even as streaming and solid‑state storage grow, optical discs remain essential for offline distribution, backup, and preservation, especially in environments where data integrity over decades is critical. Their widespread adoption also spurred standards development, influencing file formats, copy‑protection schemes, and hardware design across the digital media ecosystem.

## Notable For  
- **First digital optical format**: The Compact Disc (1979) pioneered consumer‑grade digital optical storage.  
- **High‑capacity evolution**: Blu‑ray Disc (2006) increased capacity to 25 GB per layer, supporting high‑definition video.  
- **Archival reliability**: M‑Disc and Archival Disc are engineered for data lifespans of 50 years or more.  
- **Universal compatibility**: Optical disc drives are built into most personal computers and many consumer electronics.  
- **Diverse ecosystem**: Supports a wide range of specialized formats (e.g., MP3 CD, CD+G, Ultra HD Blu‑ray) for audio, video, and data applications.  

## Body  

### Definition and Core Technology  
- An optical disc stores data as a pattern of pits (depressions) and lands (flat areas) on its surface.  
- A low‑power laser in an optical disc drive reflects off these features; variations in reflected light are interpreted as binary 0s and 1s.  

### Physical Characteristics  
- **Shape**: Circular disk.  
- **Materials**: Typically polycarbonate substrate with a reflective aluminum or gold layer and a protective lacquer coating.  
- **Standard diameters**: 120 mm (full‑size) and 80 mm (mini).  

### Major Formats and Variants  
| Format | Year Introduced | Typical Capacity | Primary Use |
|--------|----------------|------------------|-------------|
| LaserDisc | 1978 | 30–60 min video per side | Analog video playback |
| Compact Disc (CD) | 1979 | 700 MB (≈ 80 min audio) | Audio, data |
| DVD | 1995 | 4.7 GB (single‑layer) | Video, data |
| Blu‑ray Disc | 2006 | 25 GB (single‑layer) | HD video, data |
| M‑Disc | 2012 | 25 GB (BD‑M‑Disc) | Long‑term archival |
| Archival Disc | 2016 | 300 GB (dual‑layer) | Professional archival |

Specialized families include MP3 CD (compressed audio), CD+G (graphics), Ultra HD Blu‑ray (4K video), and Nintendo optical disc (gaming).  

### Usage and Devices  
- **Optical disc drives**: Integrated in PCs, laptops, game consoles (e.g., Wii, PlayStation), and standalone players.  
- **Read‑only vs. recordable**: Formats range from read‑only (e.g., commercial DVDs) to recordable/re‑writable (e.g., DVD‑RW, BD‑RE).  

### Historical Development  
- Early research in the 1960s explored laser reading of data; commercial adoption began with LaserDisc (1978) and CD (1979).  
- The 1990s saw DVD replace CD for video, while the 2000s introduced high‑definition Blu‑ray.  
- Recent focus shifted to archival stability (M‑Disc, Archival Disc) as digital preservation became a priority.  

### Standards and Classification  
- **Wikidata subclass**: optical storage, machine‑readable medium, computer storage media, removable media.  
- **Identifiers**: BabelNet 00059212n, Freebase /m/0bctr, UNESCO thesaurus concept 6105, Library of Congress sh86004405.  

## Schema Markup  
```json
{
  "@context": "https://schema.org",
  "@type": "Thing",
  "name": "Optical disc",
  "description": "A flat, usually circular, removable medium that stores binary data using laser‑readable pits and lands, used for physical data distribution and long‑term archival.",
  "url": "https://en.wikipedia.org/wiki/Optical_disc",
  "sameAs": [
    "https://en.wikipedia.org/wiki/Optical_disc"
  ],
  "additionalType": "ComputerStorageMedia"
}

## References

1. [Nuovo soggettario](https://thes.bncf.firenze.sbn.it/termine.php?id=1388)
2. Nuovo soggettario
3. Freebase Data Dumps. 2013
4. BabelNet
5. National Library of Israel
6. KBpedia
7. [OpenAlex](https://docs.openalex.org/download-snapshot/snapshot-data-format)