What Is Write-Only Memory?

Write-Only Memory (WOM) is a joke concept referring to computer memory that can be written to, but never read. Since this would be logistically counterproductive, manufacturers do not actually produce write-only memory. There may be cases when errors with hardware or software design result in a situation where data can be written to an area that is not accessible. These issues are typically caught in the course of testing and addressed so they don’t become frustrating for users.

According to legend, the write-only memory hoax started at manufacturing firm Signetics, where an engineer who was frustrated that documentation wasn’t being read created its specifications. The goal was to determine whether the review process would catch the clearly bogus standards for a product the company didn’t make and wouldn’t, since it had no practical use. These were allegedly distributed to customers, who called for more information, alerting the company to the fact that it had unwittingly sent out joke documentation.

In April 1972, Signetics took out a two page advertisement for its write-only memory products as a practical joke. The advertisement included technical drawings as well as a list of gibberish specifications like “V^cc=+10 volts.” Footnotes intended to mimic those found in other technical advertisements were included, with comments like “For the filaments, what else!” and “Final until we get a look at some actual parts.” Numerous copies were circulated by amused engineers and products designers, and can be found archived on several websites for people interested in viewing it.

Practical jokes are not uncommon at technology and Internet companies, and many involve spoofs of this nature, marking products and services that don’t exist and would be highly impractical if they did. Some include references that will only be comprehensible to members of the industry, or involve inside jokes that may be unfamiliar to everyone but people who work for a given company or department. Lack of communication between engineers and other members of design teams can be an ongoing issue, and is a not infrequent subject of jokes as a result.

While Signetics didn’t actually plan to produce write-only memory, and neither are other manufacturers, the legend lives on. Engineers can also use the term disparagingly in discussions of devices that have failed and are storing data improperly or inaccessibly. Their references suggest that while the system appears to be perfectly capable of writing the data, locating it later may be an impossible task because of memory corruption or another problem, making it as useful as write-only memory.