http://www.tomshardware.com/picturestory/476-6-seagate-hard-drive.html
“If the read/write head [of a hard disk] were a Boeing 747, and the hard-disk platter were the surface of the Earth: The head would fly at Mach 800 At less than one centimeter from the ground And count every blade of grass Making fewer than 10 unrecoverable counting errors in an area equivalent to all of Ireland. ”