The Therac-25 Incident (2021)

(thedailywtf.com)

449 points lemper | 1 comments | 27 Aug 25 06:57 UTC | HN request time: 0s | source

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haunter ◴[27 Aug 25 10:18 UTC] No.45037613[source]▶

My "favorite" part:

>One failure occurred when a particular sequence of keystrokes was entered on the VT100 terminal that controlled the PDP-11 computer: If the operator were to press "X" to (erroneously) select 25 MeV photon mode, then use "cursor up" to edit the input to "E" to (correctly) select 25 MeV Electron mode, then "Enter", all within eight seconds of the first keypress and well within the capability of an experienced user of the machine, the edit would not be processed and an overdose could be administered. These edits were not noticed as it would take 8 seconds for startup, so it would go with the default setup

Kinda reminds me how everything is touchscreen nowadays from car interfaces to industry critical software

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hiccuphippo ◴[27 Aug 25 12:44 UTC] No.45038883[source]▶

>>45037613 #

And we have a concept, optimistic updates, for making the ui look responsive while the updates happen in the background and reconcile later. I can only hope they know when not to use it.

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1. kevincox ◴[28 Aug 25 20:10 UTC] No.45056513[source]▶

>>45038883 #

Optimistic updates should almost always be paired with some sort of indicator showing if/when a value has actually been persisted. In practice this is rarely implement. Even failures are often not shown and value rolled back. (Making it a very optimistic update indeed)

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