An Anonymous Patron writes The Observer has this story on Google.
"The computing engine that powers Google is the largest cluster of Linux servers in the history of the world. One university presentation, for example, claimed that Google handled 150 million queries a day, and 1,000 per second at peak times. They also claim to have '4+ petabytes' of disk storage, and have let slip that each server is fitted with two 80 gigabyte hard drives. Now a petabyte is 10 to the power of 15 bytes, so if Google had only 10,000 servers, that would come to 400 Gb per server."