--- title: Odd Comments and Strange Doings in Unix | daily.dev description: A firsthand account from a Unix pioneer explaining the origins of two famous pieces of Unix lore: the cryptic error message 'values of β will give rise to... canonical: https://daily.dev/posts/odd-comments-and-strange-doings-in-unix-mxq3migig twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Odd Comments and Strange Doings in Unix | daily.dev og:description: A firsthand account from a Unix pioneer explaining the origins of two famous pieces of Unix lore: the cryptic error message 'values of β will give rise to... og:url: https://daily.dev/posts/odd-comments-and-strange-doings-in-unix-mxq3migig og:image: https://api.daily.dev/og/posts/mXq3mIGig.png og:image:alt: Odd Comments and Strange Doings in Unix og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Odd Comments and Strange Doings in Unix **[Lobsters](https://daily.dev/sources/lobsters)** · 7 min read · 0 upvotes · 0 comments ## Summary A firsthand account from a Unix pioneer explaining the origins of two famous pieces of Unix lore: the cryptic error message 'values of β will give rise to dom!' found in mv.c of Sixth Edition Unix, and the notorious comment 'You are not expected to understand this' in the kernel's process-switching code. The author reveals the beta message originated from a typist accidentally printing a fragment of a patent application on a Model 37 Teletype in the early 1970s. The 'you are not expected to understand this' comment is clarified as a humble admission — the authors genuinely didn't understand the broken savu/retu process-exchange mechanism, which failed when porting to the Interdata due to differing compiler register-save conventions. Additional anecdotes cover an undocumented PDP-11 division routine bug and a hardware wiring error in the KS-11 memory mapping unit discovered via circuit drawings. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What is the origin of the Unix comment 'You are not expected to understand this'? The comment was written as a humble admission, not a challenge — the authors genuinely did not understand the savu/retu process-exchange mechanism they were using. The mechanism was fundamentally broken because it depended on switching to a previous stack frame and executing function return code in a different procedure. It worked on the PDP-11 due to consistent compiler behavior but failed when porting to the Interdata, where procedure return code differed by register usage. _Developers curious about Unix internals and systems history find deep dives like this through daily.dev._ ### Where did the Unix error message 'values of beta will give rise to dom' come from? The phrase originated when a typist at Bell Labs accidentally interrupted a printout of a patent application on a Model 37 Teletype in the early 1970s, leaving a fragment visible — likely from something like 'varying values of beta will give rise to domain wall movement.' The striking, context-free phrase was later immortalized in the v6 Unix source, most likely by Bob Morris or Ken Thompson. _Unix history threads like this surface regularly for systems programmers on daily.dev._ ## Similar posts on daily.dev - [Math is hard](https://daily.dev/posts/math-is-hard-g7pgrr2pz) · Hacker News · 0 upvotes · 0 comments - [How can you not be romantic about UNIX domain sockets?](https://daily.dev/posts/how-can-you-not-be-romantic-about-unix-domain-sockets--sox4kolgg) · Lobsters · 0 upvotes · 0 comments - [Casey Muratori: Surprises In Computer History And Where Bad Code Comes From](https://daily.dev/posts/casey-muratori-surprises-in-computer-history-and-where-bad-code-comes-from-htya9hnlf) · The Developing Dev · 12 upvotes · 0 comments --- Tags: [#unix](https://daily.dev/tags/unix), [#computing-history](https://daily.dev/tags/computing-history) [View this post on daily.dev](https://daily.dev/posts/odd-comments-and-strange-doings-in-unix-mxq3migig) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Odd Comments and Strange Doings in Unix","url":"https://daily.dev/posts/odd-comments-and-strange-doings-in-unix-mxq3migig","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/odd-comments-and-strange-doings-in-unix-mxq3migig"},"datePublished":"2026-08-11T19:28:57.918Z","dateModified":"2026-08-11T19:29:26.948Z","description":"A firsthand account from a Unix pioneer explaining the origins of two famous pieces of Unix lore: the cryptic error message 'values of β will give rise to...","image":"https://media.daily.dev/image/upload/s--OHB84bZF--/f_auto/v1722860399/public/Placeholder%2010","thumbnailUrl":"https://media.daily.dev/image/upload/s--OHB84bZF--/f_auto/v1722860399/public/Placeholder%2010","isAccessibleForFree":true,"articleSection":"Lobsters","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Lobsters","logo":"https://media.daily.dev/image/upload/s--tl8v_Fku--/f_auto,t_logo/v1698841318/logos/lobste.jpg","url":"https://daily.dev/sources/lobsters"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/odd-comments-and-strange-doings-in-unix-mxq3migig","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"unix,computing-history","timeRequired":"PT7M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Lobsters","item":"https://daily.dev/sources/lobsters"},{"@type":"ListItem","position":3,"name":"Odd Comments and Strange Doings in Unix"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/odd-comments-and-strange-doings-in-unix-mxq3migig#faq","mainEntity":[{"@type":"Question","name":"What is the origin of the Unix comment 'You are not expected to understand this'?","acceptedAnswer":{"@type":"Answer","text":"The comment was written as a humble admission, not a challenge — the authors genuinely did not understand the savu/retu process-exchange mechanism they were using. 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