Hard disks have large storage capacities and extremely rapid retrieval speeds.
It is because of this that they are very popular for computer applications and in cases where rapid access to information is necessary. A hard disk is a rigid platter made of plastic or metal and is coated with a metal oxide material on which data are stored on both sides of the disk as magnetised dots. Disk drives can have several stacked disks which have multiple access arms extending between the disks. Information is stored in addressable sections of the hard disk, which is divided into a series of concentric circles.