A hard drive is constructed basically of a sealed metal housing that protects magnetically coated platters, a group of read/write heads and an electrical motor. In combination, these elements are used to both read and write data to the surface of a platter, which is the basic means of storage for many computers.

Controlled by both a logic board and a controller card, a hard drive receives commands from the computer to read and write data to the platters, which in turn is translated into mechanical movement. When the computer requests that a string of data is written to a hard drive, the logic board instructs the write heads to align the magnetic field of particles that are located on the platters surface. This in turn results in data being written to the hard drive, and can be retrieved later by requesting that the read heads detect the polarities of the aligned particles. This process of reading and writing files is directed through a hard drive's file allocation table, which determines the physical starting location of a file, and records chains of data that describe the locations of all files on the platters. This file allocation table is also referred to when the system attempts to write new files to a platter, as it keeps track of available space as well as space already in use.