Parking the Magnetic Heads of the Hard Disk
Most hard disk drives have the particular track which is designed for landing and launch of the magnetic heads. This track is named parking zone since, although the surface of a magnetic disk and a magnetic head are designed with a glance to possible casual contacts, it is still preferable to park heads on the part of a magnetic plate surface with no data recorded. The HDD is designed for the certain quantity of parking of magnetic heads, owing to the deterioration of kinematics. In S.M.A.R.T. technology two sensors are provided for tracing this parameter. The first one traces the number of connections to power supplies, and the second one determines the number of the runs of the spindle motor without disconnecting from power supplies, e.g. at an exit of the disk drive from the power-saving mode.
All the hard drives are provided with the mechanism of automatic parking at power supply turn off. Usually, the auto parking is carried out by the kinetic energy of magnetic disks rotation. At de-energization, the spindle motor is used as the generator, and the energy extracted from its windings is used for moving the magnetic heads to park position before lowering the speed of rotation below the critical level at which magnetic heads start to touch the disk surface. After heads reach the parking zone, the blocking of the system of positioning by a magnetic latch (a small constant magnet) is performed, and a smooth landing of heads to the magnetic disk surface is carried out. In modern storage devices, the alternative method is applied - instead of allowing magnetic heads to fall to a surface, heads are completely removed from magnetic disks on a particular parking platform. At power-up the disks are being spun to the constant speed, then heads "fly down" from the platform on a surface of plates which turns at speed high enough to avoid the contact of the heads with magnetic plates.