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Comment by sp332 | Hacker News Reader

Does anyone have a link to the version where the Black Team member found a bug in rigourously (mathematically) proven code? edit Ah, here it is: http://www.penzba.co.uk/GreybeardStories/TheBlackTeam.html

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That's almost exactly one of the parables between Achilles and the Tortoise that Hofstadter gives in Godel, Escher, Bach, where the Tortoise keeps breaking Achilles' record player by playing records of the machine's resonant frequency. Hofstadter gives it as an example of the 2nd Incompleteness Theorem, that in any mathematical system there are always statements that can neither be proven true nor false using the system's axioms (although I'm not fully convinced this resonant frequency example is actually an example of Godel's theorem).

In any case, that's funny, I bet Hofstadter based the example on this story of the Black Team.

While I don't know the veracity of that particular story (and the "in front of the press" bit seems really unlikely), the old washing-machine-sized drives could indeed walk across a room due to seeking, at least according to the Jargon File: http://www.catb.org/jargon/html/W/walking-drives.html .

It's a law of nature that you can build up a lot of energy in something by adding just a tiny bit of energy each pass. This was a bitter team that was beaten and decided to use physics to add this tiny bit of energy each time the tape rewound--mind you, at a steady rate chosen to add in the energy perfectly-- to embarrass somebody who had beaten them.

Or is my understanding of a tape drive incorrect, and they would wind and unwind at a set rate? Because the original article said that it would often stop, rewind, move forward to retrieve data.

I don't think it really wound all the way to the ends of the tape, like my link said. I think it just wound forward for a set amount of time, and then back, to match the resonant frequency of the device.

Also, I think the point is that it's the Black Team's job to minimize bugs shipped, and they were really impossibly good at it. It was the programmers' job to write bug-free code, and this guy was inspired by the Black Team to write perfect code. It seems like both sides were doing exactly what they were supposed to do.

On the other hand any physical system in motion is also loosing energy constantly to friction, air resistance, and other factors. Because of that and because the winding/unwinding description seemed implausible I strongly suspect the story is apocryphal.

Sorry to nitpick, but I think this is a good thing to know. Apocryphal means "of doubtful authenticity", not mythical or false, which is the how you seem to be using it. The story is clearly apocryphal.

No need to be sorry, I'll know to use it correctly in the future. :)

I think you're underestimating how mechanical old hardware really was.

There's the classic story of "Walking Drives" from esr/jargonfile:

http://dictionary.die.net/walking%20drives

Or search for "washing" here for the story about huge DEC drives being ripped apart: http://www.rinkworks.com/stupid/cs_drives.shtml

Old hardware employed a lot of force, so "bad things" (TM) really could happen.

Normally you'd expect the Q factor of a standing tape drive to be small enough that you'd be unable to come anywhere close to knocking it over with the tiny kicks from the reels.

Wouldn't you have said the same thing of the Tacoma Narrows Bridge?

I probably would, yeah, unless I actually took the time to examine the design and calculate Q. I'd've been wrong in that case.

Actually, I probably wouldn't, because if it had occurred to anyone that they ought to ensure that the bridge design had no high-Q vibrational modes, the problem would have been found and averted before the first caisson was sunk.

I have the sudden urge to build a weighted cabinet and see if I can knock it over with fast-forwards/rewinds. I've got a couple engineer friends who could run the numbers, but nothing would quite compare to the satisfaction I would feel if I could actually do it.

Can't we get Mythbusters to do it?

I think that's actually a great idea. Anyone know how to throw suggestions their way?

Here's the message board that takes submissions for Historical "Fact" myths. http://community.discovery.com/eve/forums/a/frm/f/9551919888

Exactly. How much of IBM's money had gone into developing the new product? How many sales did they lose as a result of this public humiliation?

That's the problem with "elite" teams in organizations. You don't get the actual elite. You just get the best connected, and they think they're untouchable.

"Beware of bugs in the above code; I have only proved it correct, not tried it." -- Donald Knuth

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