### Taking pi to new frontiers

American, Japanese compute pi to 5 trillion digits on one powerful desktop PC

PI IN THE SKY. Pi, the infinite number that represents the ratio of a circle’s circumference to its diameter, has long held a fascination for people, even outside the sphere of mathematics.

It’s turned up in a poem by a Nobel laureate, a song by the singer Kate Bush in which she sings pi to 150 decimal places (and, apparently, gets some of them wrong) and sporting-event cheers at the Massachusetts Institute of Technology.

And seeing how far one could go in computing pi’s digits has been something of a sport itself among mathematicians, dating at least as far back as Archimedes.

After centuries of computing pi by hand, John Wrench and Levi Smith achieved a breakthrough in 1948, calculating pi to 1,120 decimal digits using a gear-driven calculator. When electronic computers came along, the numbers got longer, and earlier this month, the bar was raised again.

Alexander Yee and Shigeru Kondo, an American computer science student and a Japanese systems engineer, reported on the site Numberworld that they had achieved a new world record, computing pi to 5 trillion digits on a single desktop PC.

And this was no ordinary desktop PC. It was a machine built by Kondo with a 3.33 GHz 2 x Xeon X5680 processor (12 physical cores, 24 hyperthreaded), 96G of DDR3 RAM and three hard drives. It was running Windows Server 2008 R2 Enterprise x64. Yee wrote that their goal was to test the limits of hardware as much as it was to compute pi. Even with all that power, the computation took 90 days. When they were finished, the compressed output of decimal and hexadecimal digits took up 3.8T, they reported.

Computing to that many digits might not have a lot of practical applications — you’d need a mere 39 digits of pi to make a circle the size of the observable universe accurate to within one hydrogen atom, according to the Wikipedia entry on pi – but it’s the sport that counts. How often does anyone get to chase the infinite?

Kevin McCaney is a former editor of Defense Systems and GCN.