write once
Of a type of storage technology in which data, once written, cannot be erased or modified.
write once: data locked in permanently after recording
Write once storage is a data recording technology where information, once committed to the medium, becomes permanent and unalterable. The mechanism prevents any subsequent erasure, overwriting, or modification of recorded data. This immutability is enforced at the hardware level, not by software permission alone, making it impossible for any user or process to change or delete what has already been written.
The most common industrial implementation is WORM (write once, read many) optical media, typically in DVD or CD form. These use a laser to burn data into a dye layer or create physical pits in the polycarbonate substrate. Once burned, that physical change cannot be reversed. Other write once technologies include certain flash memory architectures and specialized magnetic tape formats used in archival systems, where data blocks can be written once and then locked against further modification.
Write once storage solves a specific industrial problem: creating tamper-proof records. In regulated industries such as pharmaceuticals, aerospace, and healthcare, write once media provides evidence that data has not been altered after creation. If an audit trail or original measurement must remain unchanged as proof, write once is the standard approach. The data remains readable indefinitely but cannot be falsified retroactively.
Practical constraints and failure modes
Write once media demands careful planning because mistakes are permanent. A miscalculation, corrupted file, or wrong dataset written to the media cannot be corrected or removed. Optical discs also suffer from degradation over decades; the dyes used in recordable DVDs typically remain stable for 20 to 50 years depending on storage conditions and manufacturing quality, but deterioration is inevitable. Write once is therefore best paired with redundant copies stored separately and regular data migration before media ages.
In contrast to rewritable media, which offers flexibility but creates audit and security risks, write once enforces data integrity through physics rather than policy. This makes it valuable for legal discovery, compliance documentation, and long-term archives where the immutability itself is the point. However, it is unsuitable for active databases, working files, or any application requiring correction or update.