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Write once read many

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Write once read many

Write once read many (WORM) describes a data storage device in which information, once written, cannot be modified. This write protection affords the assurance that the data cannot be tampered with once it is written to the device.

On ordinary (non-WORM) data storage devices, the number of times data can be modified is limited only by the lifespan of the device, as modification involves physical changes that may cause wear to the device. The "read many" aspect is unremarkable, as modern storage devices permit unlimited reading of data once written.[Note 1]

History

WORM drives preceded the invention of the CD-R and DVD-R. An example was the IBM 3363.[1] These drives typically used a 12 in (30 cm) disk in a cartridge, with an ablative optical layer that could be written to only once, and were often used in places like libraries that needed to store large amounts of data. Interfaces to connect these to PCs also existed.

Punched cards and paper tape are obsolete WORM media. Although any unpunched area of the medium could be punched after the first write of the medium, doing so was virtually never useful. Read-only memory (ROM) is also a WORM medium. Such memory may contain the instructions to a computer to read the operating system from another storage device such as a hard disk. The non-technical end-user, however, cannot write the ROM even once, but considers it part of the unchangeable computing platform.

Current WORM drives

The CD-R and DVD-R optical disks for computers are common WORM devices. On these disks, no region of the disk can be recorded a second time. However, these disks often use a file system based on ISO 9660 that permits additional files, and even revised versions of a file by the same name, to be recorded in a different region of the disk. To the user of the disk, the disk appears to allow additions and revisions until all the disk space is used.

A version of the Secure Digital flash memory card exists in which the internal microprocessor does not allow rewrites of any block of the memory.

The Memory Vault product of SanDisk is a thumbdrive-like consumer device that functions as a WORM device, by not providing the capability of deleting any file previously written to it.[2]

Since 2005 WORM is also an option for high density magnetic tape storage devices developed by the LTO Consortium.

In 2013, GreenTec-USA, Inc. developed WORM hard disk drives in capacities of 3 TB and greater. Prevention of rewrite is done at the physical disk level and cannot be modified or overridden by the attached computer.[3][4]

Research

In recent years there has been a renewed interest in WORM based on organic components, such as RFID tags.[10]

Notes

  1. ^ Historical exceptions include time-limited discs such as Flexplay, designed for short-term rental of movies; and early non-volatile memory technologies such as magnetic-core memory and bubble memory, from which reading data also erased it.

References

  1. ^ IBM 3363 Optical WORM drive
  2. ^ "SanDisk Memory Vault Technology". SanDisk. 2011-09-14. Retrieved 2012-04-16. 
  3. ^ "GreenTec-USA, Inc. WORM Read Only Disk Drives" http://www.greentec-usa.com
  4. ^ "Best Practices to Secure Data from Modification: Eliminating the Risk to Online Content" http://greentec-usa.com/wp/GreenTec-WORM-Whitepaper.pdf
  5. ^ Organic-inorganic heterojunction WORM memory
  6. ^ "A polymer/semiconductor write-once read-many-times memory"et al.Möller
  7. ^ Smith and Forrest "A low switching voltage organic-on-inorganic heterojunction memory element utilizing a conductive polymer fuse on a doped silicon substrate"
  8. ^ Lin and Ma "Realization of write-once-read-many-times memory devices based on poly(N-vinylcarbazole) by thermally annealing"
  9. ^ "An Organic-Based Diode–Memory Device With Rectifying Property for Crossbar Memory Array Applications"et al.Teo
  10. ^ "Holst Centre reports major step towards organic RFID"
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