Of potential interest to the list:
Why computers are like the weather
* 11 July 2005
* NewScientist.com news service
IF YOU think the complex microchips that drive modern computers are
models of deterministic precision, think again. Their behaviour is
inherently unpredictable and chaotic, a property one normally associates
with the weather.
Intel's widely used Pentium 4 microprocessor has 42 million transistors
and the newer Itanium 2 has no fewer than 410 million. "Their
performance can be highly variable and difficult to predict," says
Hugues Berry of the National Research Institute for Information and
Automation in Orsay, France.
Berry, Daniel Perez and Olivier Temam say that chaos theory can explain
the unpredictable behaviour. The team ran a standard program repeatedly
on a simulator which engineers routinely use to design and test
microprocessors, and found that the time taken to complete the task
varied greatly from one run to the next.
But within the irregularity, the team detected a pattern, the
mathematical signature of "deterministic chaos", a property that governs
other chaotic systems such as weather. Such systems are extremely
sensitive - a small change at one point can lead to wide fluctuations at
a later time. For complex microprocessors, this means that the precise
course of a computation, including how long it takes, is sensitive to
the processor's state when the computation began
(www.arxiv.org/nlin.AO/0506030 <
http://www.arxiv.org/nlin.AO/0506030>).
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