Hard disks save files by altering the magnetic charge of the disk’s surface to represent 1s and 0s. Hard dicks retrieve data and programs by reading these from the magnetic disk. Characters are represented by positive and negative charges using the ASCII, EBCDIC, or Unicode binary codes. For example, the letter A would require a series of 8 charges can be packed next to one another on the disk.

Hard disk use rigid metallic platters that are staked one on top of the another. Hard disk store and organize files using tracks, sectors, and cylinders. Tracks are rings of the concentric circles without visible grooves. Each track is divided into invisible wedge-shaped sections called sectors. A cylinder runs through each track of a stack of platters. Cylinders are necessary to differentiate files stored on the same track and sector of different platters. When a hard disk is formatted, tracks, sectors, and cylinders are assigned.

Hard disks are sensitive instruments. Their read/writer heads ride on a cushion of air about 0.0000001 inch thick. It is so thin that a smoke particle, fingerprint, dust or human hair could cause what is known as a head crash.