PiFast is presently the fastest program for Microsoft Windows to compute digits of Pi. On an Athlon XP 2000+ underclocked to 1620 mhz, it computes one million digits in 4.75 seconds. It can also compute other irrational numbers like e and sqrt2. PiFast can work at lesser efficiency with very little memory (down to a few tens of megs to compute well over 109 digits).
This closed source freeware tool is a popular benchmark in the overclocking community, and has been used to compute over 20 billion (2x1010) digits of pi (the present record on a desktop computer).
