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Funny Software Engineering Morals
Posted by: jungsonn
Date: December 21, 2006 02:53AM

I though this was pretty funny:


The Pentium Chip Error, 1994
Not enough numbers in the table.

The Pentium Chip used a look-up table to do division; basically it uses a pre-calculated set of numbers to speed things up. The look-up table should have contained 1066 elements, but when the numbers were downloaded a bug in the software only put in 1061 of them. No one checked, and the chip went to manufacture with those numbers missing. When the mistake was found the chips had to all be replaced. The cost was more than $4 billion.


USS Yorktown Stops, 1998
A big something caused by nothing.

Dividing by zero is a bad idea. The answer doesn't exist. However a crewmember of the computer controlled guided-missile cruiser USS Yorktown mistakenly entered a zero on their console. It resulted in the computer program trying to do an impossible divide by zero. The program crashed and caused a failure in other linked computer systems on the ship, eventually shutting down the ship's engines, leaving it drifting for hours.
The moral: always check numbers are as expected.


AT&T Crash, 1990
The day the phones stopped working...all of them.

In late 1989, AT&T engineers upgraded the software of their 114 US switching centres: the computers that make the connections so your phone links to the one you are calling. Each computer was duplicated so if one went wrong the other would take over. On January 15th 1990, they stopped working: 70 million calls failed. The problem was in a single line of code out of millions...and it was in both computers' copies. AT&T lost $1 billion as customers fled to their competitors.
The moral: With software, duplication doesn't always help.


Mars Climate Orbiter, 1999
A weighty problem in space.

Programmers work in teams to build software for a space mission. Unfortunately for NASA's $125 million Mars Climate Orbiter, two teams didn't know what the other was up to. One team was using Imperial weight measures (pounds). The other was using metric (kilograms). The mistake wasn't found until, when finally in space, the two programs spoke to each other, got very confused and caused the spacecraft to become lost in space.
The moral: software engineering is also about team communication


The missing American Patriot Missile, 1991
A problem with bad timekeeping.

In 1991, during the first Gulf War, an American Patriot Missile battery in Dharan, Saudi Arabia, failed to shoot down an incoming Iraqi Scud missile. The Scud missile hit an army barracks with many casualties. State-of-the-art computers controlled the Patriot missile, but there was a problem. To work Patriot needed to accurately know the time. This was done with an internal clock that started to tick when the computer was first switched on. However the computer program, when converting the internal clock time into the time used by the guidance system introduced a tiny mistake. It rounded the number down slightly. With each passing second the error became larger until finally it was enough to make the missile miss.
The moral: small mistakes in calculations often build into big mistakes.


And Finally (expect the unexpected)
Bugs can kill.

In the early days of electronic computers they used relays, electromechanical switches that rocked up and down to switch the electrical circuits. Grace Murray Hopper, who was in charge of the team working with the Mark II computer, (an early electromechanical device), found that a moth had flown through the window and blocked one of the relays, so shutting the system down. This is arguably where the term computer 'bug' comes from.
The moral: The things some moths get into can be shocking!

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Re: Funny Software Engineering Morals
Posted by: jungsonn
Date: December 21, 2006 03:03AM

I forgot the copyright link: http://www.dcs.qmul.ac.uk/cs4fn/

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Re: Funny Software Engineering Morals
Posted by: rsnake
Date: December 21, 2006 10:21AM

That's very true... The off by one errors or rounding errors are some of the hardest bugs to catch.

- RSnake
Gotta love it. http://ha.ckers.org

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Re: Funny Software Engineering Morals
Posted by: jungsonn
Date: December 21, 2006 10:39AM

Ghehe.. most of them I knew, only that story about the pentium was pretty new to me.

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