Thursday, June 11, 2009

Question - 267

Connect the key rings to the equation in the right.

Answer: The equation is the expression for Brun's constant which is the sum of reciprocals of twin primes (primes p such that p+2 is a prime as well). This constant is often studied in relation to the conjecture that there are infinitely many twin primes (for ex., irrationality of the constant would prove the conjecture). Thomas Nicely, a math professor, was using a cluster of computers to evaluate the constant when he noted some inconsistencies which he ultimately traced down to the Intel pentium chipset. Due to some missing values in a look up table, the chip was returning erroneous outputs for very few operations. Intel's handling of the crisis was heavily criticized leading to the recall of all processors using the chip. Andy Grove, then CEO of intel, made a few of these chips into keychains as a memento. Rajeev, nice try, Avi and adityam got it. Well done.

4 comments:

rajeev said...

andy grove. pentium FDIV bug found during twin prime computations.

nice try said...

andy grove, intel floating point bug?

Avi said...

Thats the formula for Brun's constant, the number to which the sum of the reciprocals of twin primes would converge to.. (Defn shamelessly ripped off of Wikipedia).
It was while trying to estimate the value of Brun's constant that a minor bug in Intel's floating point calculations was discovered, leading to a big hue and cry and eventually a "on demand" replacement of the defective chips. Some of the recalled chips were made into key-rings as keepsakes.

Anonymous said...

Intel's Pentium FDIV error. The formula on the right is sum of reciprocals of twin primes. The bug was discovered when someone was computing this number and noticed that something is wrong, and after a lot of debugging found that the chip was at fault (try using that explanation the next time your program does not work). The key chain was issued by Intel after the bug was made public. The quote is by Andy Grove, a former Intel CEO