Optical Ablation. A permanent recording mechanism used in early WORM optical disk systems, where data is written by physically removing or altering the recording layer of the media.

A (usually) flat, circular recording medium whose data-bearing surface is exposed and not permanently enclosed within a protective housing.

A recording medium where the data-bearing disc is completely enclosed — either permanently or removably — within a protective cartridge, casing, sleeve, or hard shell.

Any of a number of data storage formats that consist of an optical disc enclosed in a protective cartridge.

Optical Memory Disk Recorder. A professional class of high-capacity, magneto- optical recording systems and media used for digital data archiving, medical imaging, and broadcast video mastering.

Write-Once, Read-Many. A class of optical storage media where data can be written only a single time to a specific sector. Once recorded, the data becomes permanent, immutable, and cannot be overwritten, modified, or deleted.