How does a Hard Disk Drive Store Data?

All information located on a computer is expressed as a series of ones and zeros (1/0), as binary digits (bits). Taking advantage of the nature of magnetic particles, that they can be polarised to magnetic north or south and that their magnetic poles can be alternated or switched when a sufficient magnetic field of the correct polarity is applied, Hard Disk Drives can store the very same sequence of bits onto a disk by polarising the required magnetic particles on the recording medium such that they represent the data being stored. Hard Disk Drives are sectioned off such that they contain both intersecting tracks and sectors. The purpose of which is to provide a logical data structure, to provide a way to distinguish between areas of data. Within each track there are a number of sectors. It is within these sectors of the Hard Disk which data is stored.

The platter of a Hard Disk Drive is coated with a magnetically sensitive coating comprised primarily of magnetically charged particles or filings which as a whole may be called the recording medium. These particulates can be magnetically aligned such that they represent binary digits, by inducing an electromagnetic field upon them via a devices read/write head. The recording media contains many billions of microscopic particles which when viewed extremely close resemble miniature metal filings. When a Hard Disk Drive records data onto the medium it takes many hundreds (usually anywhere from 500 to 100) of these magnetically sensitive particles to store a single binary digit. The increased reduction of the amount of particles required to record data is highly limited by the precision of the read/write head (the miniature device that reads and records data onto the recording medium) because the magnetic field which is used by the drive’s read/write head to read and/or record (write) data is such that it already tentatively borders nearby data.

Should it be shrunk much further in an attempt to increase precision, the likelihood of data corruption would increase vastly. Research by various parties has been on-going to find a workable solution to recording data onto much fewer or even single particles for some time now. A hard drive may record data onto the Hard Disk Drive by applying a sufficient magnetic field to the section of the recording medium (which is suspended upon the Hard Disks platter) such that the data (a series of ones and/or zeros which correspond to the information being stored) is recorded onto the medium by aligning the specified particles to the desired magnetic pole (north or south). In doing so, any previous data which was present is therefore destroyed.

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Perpendicular vs Longitudinal

Ever since the late 1980’s and early 1990’s magnetic media drive manufacturers have been researching the feasibility of switching from longitudinal to perpendicular recording techniques. The advantage is clearly one of capacity: when longitudinal magnetic particles are packed together, they take up much more space than if they were to stand upright, if they stood perpendicular to the platter. More than merely a matter of initial capacity gain, perpendicular recording technology avoids a problem which has been well known in the field for many years: the super-paramagnetic effect (SPE), which affects magnetically charged particles of such small size as that used in Hard Disk Drives. “The super-paramagnetic effect is a phenomenon observed in very fine particles, where the energy required to change the direction of the magnetic moment of a particle is comparable to the ambient thermal energy” (source: Wikipedia.org).Many theories have cropped up over the years as to what density magnetic particles (described by a disks areal density) may achieve before becoming subject to SPE. At present it is suggested that anything from 100Gbit/inch2 to 150Gbit/inch2 is the physical limitation for longitudinal Hard Disk Drives, although perpendicular media solutions have been made as high as 230Gbit/inch2.

In the layering of the magnetic particulates atop a magnetic suspension layer and orienting the particles perpendicular to the platter, the recording medium can pack many more magnetically sensitive particles together in the same space than previously possible whilst keeping SPE at bay. Perpendicular recording technology does not however preclude SPE from limiting capacity in the future, more than anything perpendicular recording technology can been described as a way to give manufacturers breathing room to develop more permanent technological solutions such as holographic lithography or a multilayered recording medium. Traditional recording media manufacture consists of the spreading of recording material over a disk platter via a centrifugal force induced by spinning the platter whilst the recording material is placed atop its surface. The centrifugal force would spread the recording material across the surface, evenly spreading it in all directions. Perpendicular recording media manufacture on the other hand requires a much different technique.