Modern Software Problems - The Technical and Social History of Software Engineering - page 360

gic. Requirements modeling would not have found the error, but it might have led
to possibly more robust error-checking protocols. Pair programming is uncertain
for this problem.
Why this problem was not found by testing, as it should have been, is an in-
teresting question. Messages between switching centers is an obvious topic for
testing. Risk-based testing with certified professional testers might have found the
problem.
1991: Patriot Missile Target Error
In spite of many successes during the first Gulf War, in 1991, a Patriot missile did
not stop an inbound Scud that landed in a U.S. base and killed 28 military person-
nel and injured 100.
The software error in the Patriot navigation and targeting routines apparently
had a rounding error that threw off timing and caused the miss.
Lessons learned: The lesson learned from this problem is that every detail needs
to be examined in mission-critical controls.
Problem avoidance: This problem would certainly have been found by code in-
spections. It might have been avoided by requirements modeling. Pair program-
ming might have found this problem, too, unless the rounding error was introduced
using borrowed or reusable code falsely assumed to be correct.
It is uncertain whether static analysis would have found this error because it
was not an error of syntax and might have been missed.
Testing should also have found this error but did not. Modern risk-based testing
might have identified the problem.
1993: Intel Pentium Chip Division Problem
In 1993, the new Intel Pentium chip was discovered after release to have a bug
when dividing with floating point numbers. The error was small, only a fraction of
a percent, and it did not actually impact very many users.
However, the error was located in about five million chips already installed and
in daily use. Intel's first response was unwise: It wanted users to prove that they
needed better accuracy than the chip provided in order to get a replacement. This
caused a public relations flap of serious magnitude. Intel relented and provided
new chips to anyone who asked for one, assuming the customer had purchased a
computer with the erroneous chip.