Magnetic disk are smooth metal plates coated on both sides with a think film of magnetic material. A set of such magnetic plates are fixed on a spindle are below the other to make up disk pack. The disk pack is mounted on a disk drive. The disk drive consists of a motor to rotate the spindle about its axis at a speed of 3600rpm. The drive also has a set of magnetic heads mounted on arms. Information is recorded on the surface of a disk as it rotates about its axis. Thus it is on circular track on each disk surface. A set of corresponding tracks in all surface of a disk pack is called a cylinder. In a disk pack the top most and bottom most surface are not used for data recording. A cylinder consists of a number of tracks. Each track is divided into sectors. Read and write operation in a disk begins on sector boundaries.
With the evolution of hard disk system, IBM (International Business Machines ) developed smaller exchangeable disk pack, larger disk packs and winchesters.
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