HDD Magnetic Head
The magnetic head is a complicated construction consisting of a set of details. These details are so small that they are made by a photolithography method, like microcircuits. The working surface of a magnetic head is polished with the same exquisite precision, as a surface of a magnetic disk. The number of magnetic heads is specified in HDD technical documentation by the manufacturer. Usually, there are from 1 to 8 magnetic heads. Installation of the head and its keeping on a magnetic track is provided by the electromagnetic positioning system.
For data recording, the inductive head is used. The head transforms digital information into a variable magnetic field which magnetizes a site of a magnetic disk. However, the inductive head is not suitable for reading the information from the disk, since it has the dependence of the amplitude of a readout signal on the speed of moving of a magnetic covering; it also has the high level of noise hampers the correct recognition of weak signals. For reading the information the magneto-resistive head MRH (Magneto-Resistive) or GMR (Giant Magneto-Resistive) is used. It is the resistor with the resistance changing depending on the intensity of a magnetic field, and the amplitude does not depend on the speed of change of a magnetic field. It allows reading out the information from a disk much more reliably and, as a consequence, it provides the considerable increase of extreme density of record. In immediate proximity to magnetic heads, there is a microcircuit which switches an active head and carries out the preamplification of a signal.
At rotating of magnetic disks, the heads rub the surface of plates in the parking zone until the speed high enough to enable the heads flying up over the surface of the air cushion is reached. In working position, the distance between magnetic heads and the surface of a magnetic disk is some parts of the micron, and the heads do not touch the surface. At power off the controller makes an automatic parking of the heads, moving them to the individual parking zone where the heads safely go down to the surface of the magnetic disk. The parking area is not used for data recording.