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The Therac-25 Incident (2021)

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Re: The Therac-25 Incident (2021)

#291

Post by Izkata »

roeles wrote: post #125
0xDEAFBEAD wrote: post #98

Earlier quoted context omitted.

Honestly I wish instead of the Therac-25, we were discussing a system which made use of unit testing and defensive coding, yet still failed. That would be more educational. It's too easy to look at the Therac-25 and think "I would never write a mess like that".

One instance that crosses my mind often is the airbus a320 incident at Hamburg in 2008. Everything was done right there, but the requirements were wrong. Despite all the procedures and tests, the software still managed to endanger the lives of the passengers.

The Boeing 737 MAX had an additional safety feature that was causing crashes due to bad input from the sensors, that pilots didn't know about so they couldn't override. This was 2018 and 2019. After the first crash, the manuals and training were updated to explain what was going on and how to override it.

https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au...

Re: The Therac-25 Incident (2021)

#293

Post by zackmorris »

dezgeg wrote: post #206
zackmorris wrote: post #184

Our power went off a couple off weeks ago due to wind probably knocking a branch into a power line. Now our Frigidaire microwave runs with the door open. Supposedly there are mechanical switches that prevent that, but evidently "modern" microwaves can control the gun through the logic board. The engineering failures that led to this, from conceptual to design to internal control, boggle my mind. I'm not even sure whe…

It's possible that it's just operating the lights and turntable without actually cooking - if you search HN you find that failure mode.

Ya that's what I'm hoping, because I've been blasted for a second or two here and there. I guess I could put a CD next to it and see if it crackles haha. But I'll probably just recycle it and move on.

Re: The Therac-25 Incident (2021)

#294

Post by bombcar »

WalterBright wrote: post #289
bombcar wrote: post #250

Earlier quoted context omitted.

Failsafe design is actually really fun when you start looking at all the scenarios and such. But one key component is that IF a failsafe is triggered, it needs to be investigated as if it killed someone; because it should NEVER have triggered. Without that part of the cycle, eventually the failsafe is removed or bypassed or otherwise ineffective, and the next incident will get you.

Most airplane crashes are due to multiple failures. The accidents are investigated, and each failure is addressed and fixed. The result is incredible safety.

People know about that; what they forget about is that any failure is noted and repaired (or deemed serviceable until repair).

Airplane reliability is from lots of failure analysis and work but also comprehensive maintenance plans and procedures.

Re: The Therac-25 Incident (2021)

#295

Post by Izkata »

Liquix wrote: post #152
skinwill wrote: post #64

Earlier quoted context omitted.

Around here we have Epic. If you want a good scare, look up their corporate Willy Wonka-esq jail/campus and their policy of zero remote work.

I thought "Willy Wonka-esque" was tongue in cheek, but they have a yellow brick road leading up to the front door... absolutely bizarre Those who want to escape the office altogether, can hop on one of the company’s 600 cow-print bikes to take meetings from a treehouse, slide down a rabbit hole or grab lunch in a train car. https://www.cnbc.com/2024/09/01/inside-epic-systems-mythical...

> but they have a yellow brick road leading up to the front door...

> The Oz office building on Epic’s campus.

You undersell it.. That's the view of the Emerald City from Quadling Country in the books, red flowers included.

Re: The Therac-25 Incident (2021)

#296

Post by lopespm »

remyporter wrote: post #164
greatgib wrote: post #60

Earlier quoted context omitted.

This story is kind of old. But also I'm suspicious that this was an AI generated content due to this weird paragraph (one becoming "they"): It's worth noting that there was one developer who wrote all of this code. They left AECL in 1986, and thankfully for them, no one has ever revealed their identity. And while it may be tempting to lay the blame at their feet—they made every technical choice, they coded every bug—…

I’ve been writing on the Internet since very early days, and have put almost twenty years into The Daily Wtf specifically. Which means I’m actually over represented in the training set. I don’t write like AI. AI writes like me.

I am really amazed by the frequency and the quality of your output.

Would you have an article on your routines, how you structure your day / work? Essentially, what enables your consistency, and quality articles?

Re: The Therac-25 Incident (2021)

#297

Post by kevincox »

hiccuphippo wrote: post #123
haunter wrote: post #75

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…

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.

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)

Re: The Therac-25 Incident (2021)

#298

Post by greazy »

NortySpock wrote: post #199
greazy wrote: post #68

Earlier quoted context omitted.

It's still an issue. I've heard stories of EMR system going down forcing staff to use pen and paper. It boggles my mind that such systems don't have redundancy. These are commercial products being deployed.

The redundancy is pen and paper. The EMR just helps teams coordinate faster, pull up records faster, etc. When I worked at Cerner years ago (now owned by Oracle), there were rumors that the Cerner EMR still could barely handle DST* spring forward, but could not handle DST fall back (where the 01:00 hour is repeated) -- you had do preemptively switch to pen-and-paper for the hours around the switch. I assume this was…

Pen and paper is back up in case of extreme events, and not because the software crashed or a bad patch was applied.

Millions on software with no software redundancy built in is insane in the medical field.

Re: The Therac-25 Incident (2021)

#299

Post by rowanG077 »

benrutter wrote: post #283
rowanG077 wrote: post #240

Earlier quoted context omitted.

I think the opposite. The only reason software quality emerges is because of good developers. It's a prerequisites. Process helps good developers deliver quality. But there is no process that allows a team of bad developers deliver quality. you can't squeeze blood from a stone.

That's true, but even so - great developers still make mistakes, and if they don't hear about production errors because of a breakdown in the customer communications from sales etc, then those mistakes will never be fixed. It's not that great developers aren't necessary for software quality, more that they aren't sufficient.

I think great developers are necessary for software quality. But indeed often not sufficient.

Re: The Therac-25 Incident (2021)

#300

Post by mnw21cam »

bobmcnamara wrote: post #237
mrguyorama wrote: post #194

Earlier quoted context omitted.

That chart is not clear. The Camry, the Solara, and the RAV4 are all the exact same engine hardware and software, at nearly all times. Especially the Solara, which is just a Camry with a shinier body. It uses an identical engine, throttle body, and ECU flash and is even considered a "Camry Solara". That Camry "Unintended accelerations" jumped while Solara didn't means that it isn't the hardware. Instead, they all sta…

> The brakes on all Toyotas are fully hydraulic No, most are hydraulic with vacuum boost. If you aren't expecting it, the increased force required to drive the brakes hydraulically from the pedal without boost assist is significant and can be surprising. I assume most folks haven't had an engine fail going downhill, but for a large pickup I was standing on the brake pedal and had to push my leg down by pulling on the…

Note that in many engines, vacuum is provided by a separate vacuum pump, which is driven by the rotation of the engine or rarely by an electric motor. This is always true for a diesel engine (because there is no intake manifold vacuum) and many petrol engines too (if they are direct injection, they also may not have sufficient intake manifold vacuum).

Even if you have a total engine failure, if you're going down a hill, if you keep it in gear then the motion will be turning the engine still, which will be generating vacuum regardless of whether that is by a separate vacuum pump or the intake manifold (unless the throttle valve also fails or you get a gaping hole in the side of your intake, but that seems unlikely).

So braking should still keep working as normal, as long as you keep it in gear and don't disengage the clutch.

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