Dennis Ritchie's collection of Unix oddities begins with the Sixth Edition mv command, which could emit the diagnostic 'values of β will give rise to dom!'. The source line used literal ASCII SI/SO control characters around a 'B' to shift a Model 37 Teletype into its extended character set, making the B print as a Greek beta.

The phrase originated in the early 1970s, when Bell Labs typists produced patent applications on Unix. Someone spotted the fragment sitting alone on a Teletype printout — almost certainly a truncated sentence about beta values and domain wall movement from some physics patent, interrupted by an ed '!' — and found it irresistible. Doug McIlroy's text-to-speech software then pronounced 'beta' British-style ('beeta') and stressed 'dom' until it sounded like 'doom'. The joke was immortalized in the v6 source, probably by Bob Morris or Ken Thompson.

Ritchie also defends the most-quoted comment in Unix history, 'You are not expected to understand this', from the v6 context-switching code. It was meant in the spirit of 'this won't be on the exam', not as a taunt — and worse, the authors didn't understand it either. The savu/retu coroutine mechanism was fundamentally broken: it relied on returning through a different procedure than the one that saved state, which only worked because the PDP-11 compiler always saved context identically. When Ritchie and Steve Johnson first ported the kernel to an Interdata machine, the code very much was on the exam; after a week of agony they rewrote the control-passing primitives entirely.

He confesses to one genuinely guilty comment: a PDP-11 32-bit division routine annotated 'this is the clever part', which he only almost understood. In a 1998 addendum, Amos Shapir points out the trick contained a real bug — it relied on undocumented behavior that later PDP-11 models (like the 11/34) changed, producing very strange results in signed-overflow cases.

Finally, a hardware story: around 1970-71, Unix ran on a PDP-11/20 with no memory protection, so users shouted 'A.OUT?' before running programs. Bell Labs ordered one of perhaps six KS-11 memory-mapping add-ons ever made, which had to special-case the KE-11A arithmetic unit's device-space addresses (777302 and up). The EAE simply didn't work — until the circuit drawings revealed an 'EAE ADDRESS DETECTED H' signal on one page meeting 'EAE ADDRESS DETECTED L' on another with nothing in between. An embarrassed Digital Special Systems engineer fixed it in the field with an unused inverter pin and some white wires.