Friday, 22 May 2015 00:00

Data recording technologies in the hard disk drives

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b2ap3_thumbnail_iStock_000022846885XSmall.jpgSeparate sites of a magnetic disk can be magnetized in one of the two possible ways, which represent zero or one i.e. 1 bit. Such magnetized area is called a magnetic domain. It is a micro-sized magnet on the surface of the hard disk, which has certain orientation of southern and northern magnetic poles. To record one bit of data, a magnetic head creates specifically directed magnetic field which orients the domain. A magnetization vector of the domain remains unchanged for a long time after the magnetic head stops affecting the magnetic surface. Storage density (amount of information which can be stored in one unit of the plate surface) depends on the size of domains. Commonly used values of storage density are:

  • BPSI (Bits Per Square Inch) – areal density – amount of information which can be stored in one square inch of the magnetic disk.
  • TPI (Tracks Per Inch) – value which shows the density of tracks stored in the magnetic plate. It is measured in tracks per inch.
  • BPI (Bits Per Inch) – linear or recording density – value which shows the density of data stored in the track. It is measured in bits per inch of a track.

Impossibility of infinite decrease of a domain size is stipulated by the following factors:

  • Size of a magnetic head. Nowadays it determines the size of the magnetized area – the domain.
  • The decrease of the readout signal level and the increase of noise level in it.
  • Spontaneous self-demagnetization of the domain caused by the thermal effect.

Besides the domain decrease technology, HDD manufacturers also utilize other methods of increasing the storage density, namely:

PRML (Partial Response Maximum Likelihood) – conversion scheme of the analog signal stored in the magnetic disk which is based on the range of concepts of the pattern recognition theory. In PRML, in order to decode a readout signal, this signal is compared to a number of patterns. That which is most similar to the original is selected. This method consists of two parts: Partial Response subsystem which converts analog signal to digital one and minimizes noises and Maximum Likelihood subsystem which carries out digital signal processing to restore its original form. This conversion scheme and its extension EPRML are used in most modern hard disk drives.

AFC (AntiFerromagnetically-Coupled) is a data storage technology which consists in covering Winchester disk with a 3-layer antiferromagnetic coating in which a special isolation layer of ruthenium is sandwiched between two magnetic layers. Since the top and the bottom domains have antiparallel orientation of the magnetic field, they form a coupled unity which is more resistant to spontaneous magnetization reversal than a single “flat” domain.

PMR (Perpendicular Magnetic Recording) is a data recording technology which delivers almost twice the storage density of traditional recording and reduces problems caused by magnetic interference. Contrary to the traditional recording technology, PMR uses magnetic domains with the magnetic field vector not parallel but perpendicular to the surface of the magnetic disk. Thus the neighboring and differing domains are aligned with similar poles (which as a rule push off from one another) directed not to one another but to the disk platter. Contrary to the traditional recording technology, PMR decreases the interdomain space, thus increasing storage capacity of hard disk drives.

Longitudinal magnetic recording


Perpendicular Magnetic Recording


HAMR (Heat Assistant Magnetic Recording) - is a data recording technology which takes advantage of high thermal stability magnetic compounds. To record data, HAMR uses laser thermal assistance to first heat a magnetic domain. Laser beam diameter determines the size of the area corresponding to one bit of information. When the magnetic domain is being heated, its coercivity reduces and the heated sites become capable of being magnetized. An effective heat sink technology (cable of cooling magnetic plates during data recording) is necessary to implement HAMR in mass production.

SOMA (Self-Organized Magnetic Array) is a technology which implies formation of the “self-organized magnetic arrays” of the smallest homogenous iron-platinum conglomerates of 3 nanometers (3 nanometers are 10-15 atoms of the solid material arranged in line). Implementation of this “nanotechnology” will contribute to the stability of magnetic grains and to the decrease in the domain size.

Last modified on Friday, 22 May 2015 14:04
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Viktor S., Ph.D. (Electrical/Computer Engineering), was hired by DataRecoup, the international data recovery corporation, in 2012. Promoted to Engineering Senior Manager in 2010 and then to his current position, as C.I.O. of DataRecoup, in 2014. Responsible for the management of critical, high-priority RAID data recovery cases and the application of his expert, comprehensive knowledge in database data retrieval. He is also responsible for planning and implementing SEO/SEM and other internet-based marketing strategies. Currently, Viktor S., Ph.D., is focusing on the further development and expansion of DataRecoup’s major internet marketing campaign for their already successful proprietary software application “Data Recovery for Windows” (an application which he developed).

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