A hard disk drive (HDD) is a non-volatile storage device that stores digitally encoded data on rapidly rotating disks with magnetic surfaces. HDD's are found in almost all modern computers and most other devices containing large amounts of data, such as online gaming systems, media centers, and digital video recorders. An HDD consists of one or more rigid platters, usually made of aluminum, glass or ceramic. Data is written to and read from the platters, usually by the recording heads which are mounted on a moveable arm. The arm moves the heads back and forth over the surface of the platters as they spin. By reading and writing data in a circular pattern, the amount of data an HDD can store and the access rate are dramatically increased.