Write-only memory (joke)

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Write-only memory (WOM) is the opposite of read-only memory (ROM). By some definitions, a WOM is a memory device which can be written but never read. Initially there seemed to be no practical use for a memory circuit from which data could not be retrieved. The concept is still 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. Signetics published some 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.[citation needed]


The datasheet was created "as a lark"[4] by Signetics engineer John G 'Jack' Curtis[5] and was inspired by a fictitious and humorous vacuum tube datasheet[6] from the 1940s. It was seen as "an icebreaker" and was deliberately included in the Signetics catalog.[5]

Roy L Twitty, a Signetics PR person, released a tongue-in-cheek press release touting the WOM on April 1, 1973.[7]

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 0±2% volt (i.e. ground). It was specified to run between 0 and −70°C.[8]


In 1982, Apple published their official Apple IIe Reference Manual (part number A2L2005),[9] which included two references to write-only memory:

On page 233:

  • bit bucket: The final resting place of all information; see write-only memory.

On page 250:

  • write-only memory: A form of computer memory into which information can be stored but never, ever retrieved, developed under government contract in 1975 by Professor Homberg T. Farnsfarfle. Farnsfarfle's original prototype, approximately one inch on each side, has so far been used to store more than 100 trillion words of surplus federal information. Farnsfarfle's critics have denounced his project as a six-million-dollar boondoggle, but his defenders point out that this excess information would have cost more than 250 billion dollars to store in conventional media.


The 1995 Computer Contradictionary book discusses 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 to and then erased, for memory re-use.[10]

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 media are "write only memory", because without efficient means of search and retrieval for video data archives, very little is viewed after recording.[11][12]

Other members of the family[edit]

The 25120 WOM joined a family of equally-useless parts made before and since. These include the dark bulb, dark-emitting diode, WAS gate, and Inoperational Amplifier.[13] Grandparents were the Umac 606 Infernal Anode Phantasatron and the Electrovoice Rearaxial Softspeaker.[14][15] Note that the Phantastron (not Phantasatron) is a real, if obsolete, circuit for generating precision sawtooth waves.

See also[edit]


  1. ^ Pease, Robert A. "The origin of the WOM – the "Write Only Memory"". National Semiconductor. Archived from the original on 10 September 2011. Retrieved 2011-11-28..
  2. ^ "Are you fooled?". China Daily. 2011-04-02. Retrieved 2011-11-28.
  3. ^ Raymond, Eric S (ed.). "write-only memory". The Jargon File. CatB. Archived from the original on 7 November 2011. Retrieved 28 November 2011.
  4. ^ Sigwom.
  5. ^ a b Sigwom.
  6. ^ Wemac 1Z2Z Slightly Tentative Data, Eitel-McCullough, Inc. 1953, itself a successor to Umac 606 Infernal Anode Phantasatron Data Sheet, Eitel-McCullough, Inc., 1950, both referenced on "Wemac 1Z2Z Data Sheet", sigwom.com. Note the reference to 'encabulitzation' in the 1Z2Z data sheet.
  7. ^ Tina (ed.), "The original papers on the invention of the best electro…", Funny pages
  8. ^ Curtis, John G ‘Jack’ (1972). "Signetics 25120 Fully Encoded, 9046xN, Random Access Write-Only-Memory" (PDF) (photocopy). Signetics. Archived from the original (PDF) on March 16, 2012. Retrieved 2012-03-16..
  9. ^ Apple IIe Reference Manual, Apple Computer, 1982, part number A2L2005, 266 pp.
  10. ^ Kelly-Bootle, Stan (1995), EWOM (Google books), p. 69, ISBN 9780262611121.
  11. ^ Laurini, Robert (2000-10-18), Advances in Visual Information Systems: 4th International Conference, VISUAL. (Google books), p. 49, ISBN 9783540411772.
  12. ^ Blitzer, Herbert L; Jacobia, Jack (2002), Forensic Digital Imaging and Photography (Google books), p. 61, ISBN 9780121064112.
  13. ^ Zener-enhanced Dark Emitting Diodes (ZeDEDs) deliver 10X more Dark per Watt, Lee Goldberg -April 01, 2015 , EDN
  14. ^ http://www.tubecollectors.org/archives/606.pdf
  15. ^ "Electro-Voice SP13.5RBXWK Rearaxial Softspeaker". steamer.mindfart.com.