Hard Drive Heads

"The dimensions of the head are impressive. With a width of less than a hundred nanometers and a thickness of about ten, it flies above the platter at a speed of up to 15,000 RPM, at a height that’s the equivalent of 40 atoms. If you start multiplying these infinitesimally small numbers, you begin to get an idea of their significance. Consider this little comparison: if the read/write head 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. "