While almost everyone is familiar with computer hard disks, only few know that the heart of the hard disk is an electrically commutated DC motor, which is known as a spindle motor. This spindle motor carries the storage disks, which it rotates around its own axis (spindle). The reading and writing heads moving over the disks can then magnetize and demagnetize the magnetic layers, thus writing or reading the digital information at extremely high speed and density on the disks in concentric circles.
If we consider the memory capacity of modern hard disks, it very quickly becomes clear that the requirements placed upon the spindle motor are quite considerable. Since the heads move over the disks at distances in the nanometer range, spindle motors have to be manufactured and packed in cleanrooms because even the smallest particle of dust would mean the immediate destruction of the hard disk, quite apart from the requirements on the mechanical precision of the components, their reliability and working life. A particular technical challenge is the design of the bearing systems, which some years ago were changed from ball bearings to fluid dynamic bearing systems due to the necessary improvement of concentric, quiet running properties. Every spindle motor has an application-specific hydrodynamic bearing system to ensure the best possible quality and reliability. Not only an extremely high running stability and running accuracy characterize a hard drive motor with FDB. The high running speeds, up to 15000 revolutions per minute and the very low noise level, are also characteristics with which the spindle motors designed by PM DM shine. The energy efficiency and the efficiency factor of such special motors are very high and because in a hard disk motor does not produce wearing parts, it is characterized by a long service life and low power consumption. The PM DM hard disk drives are used in all variations of 2.5"and 3.5" hard disk storage. Fields of applications are, besides laptops, notebooks and servers, also consumer electronics, e.g. game consoles, digital video recorders and music recorders.