> Imagine a hard drive head as a 747 flying over a grassy field at 75 miles per hour. The air gap between the bottom of the plane and the top of the grass is two sheets of paper. Now, if we measure bits on the disk as blades of grass, the track width would be 4.6 blades of grass wide and the bit length would be one blade of grass. As the plane flew over the grass it would count blades of grass and only miss one blade for every 25 thousand times the plane circled the Earth.
