Write-only memory (joke)

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Write-only memory (WOM) is the opposite of read-only memory (ROM). By definition, a WOM is a memory device which can be written but never read. Since there should be no practical use for a memory circuit from which data cannot be retrieved, the concept is most often used as a joke or a euphemism for a failed memory device. The first use of the term is generally attributed to Signetics in 1972. More recently, useful applications of write-only memory have been found.

Signetics unintentionally published write-only memory literature as the result of an inside practical joke which is frequently referenced within the electronics industry,[1][2] a staple of software engineering lexicons,[3] and included in collections of the best hoaxes.

The Signetics original[edit]

Out of frustration with the long and seemingly useless chain of approvals required of component specifications during which no actual checking seemed to occur, an engineer at Signetics once created a specification for a write-only memory and included it with a bunch of other specifications to be approved. This inclusion came to the attention of Signetics management only when regular customers started calling and asking for pricing information. Signetics published a corrected edition of the data book and requested the return of the 'erroneous' literature.[1]

Later, in 1972, Signetics bought a double-page spread in the April issue of Electronics and used the specification as an April Fool's Day joke. Instead of the more conventional characteristic curves, the 25120 "fully encoded, 9046×N, Random Access, write-only-memory" data sheet included meaningless diagrams of "bit capacity vs. Temp.", "Iff vs. Vff", "Number of pins remaining vs. number of socket insertions", and "AQL vs. selling price". The 25120 required a 6.3 VAC Vff (vacuum tube filament) supply, a +10 Vcc (double the Vcc of standard TTL logic of the day), and Vdd of zero volts (i.e. ground), ±2%. It was specified to run between 0 to -70°C.[4][5]

Further developments[edit]

Stan Kelly-Bootle in his Computer Contradictionary reports EWOM, or Erasable Write-Only Memory (an analogy of EPROM), a memory copyrighted by IBM (Irish Business Machines), which allows the data to be written into and then erased from, for memory re-use.[6]

With the explosive growth of the amount of video data available both online and in private use, there emerged a common joke that video tapes and other video data is "write only memory", because without efficient means of search and retrieval for video data archives very little is viewed after recording.[7][8]

See also[edit]


  1. ^ a b Robert A. Pease, Staff Scientist. "The origin of the WOM - the "Write Only Memory"". National Semiconductor. Retrieved 2011-11-28.  deadlink repaired and archived 26 September 2012
  2. ^ "Are you fooled?". China Daily. 2011-04-02. Retrieved 2011-11-28. 
  3. ^ "write-only memory". Jargon File. Retrieved 2011-11-28. 
  4. ^ Signetics (1972). "Signetics 25120 Fully Encoded, 9046xN, Random Access Write-Only-Memory". Retrieved 2011-11-03.  — A photocopy of the original; a digitized, better readable version here accessed 2012-9-28)
  5. ^ "write-only memory". The Jargon File. 
  6. ^ EWOM
  7. ^ Advances in Visual Information Systems: 4th International Conference, VISUAL ... - Google Boeken
  8. ^ Forensic Digital Imaging and Photography - Herbert L. Blitzer, Jack Jacobia - Google Boeken
This article includes material from the Jargon File.