| What is a Hard Disk Drive? | | | | Perpendicular verses Longitudinal |
| A Hard Disk Drive (HDD) is a device used by modern | | | | Ever since the late 1980's and early 1990's magnetic |
| computers to permanently store information. The | | | | media drive manufacturers have been researching the |
| Hard Disk Drive is arguable the most essential part of | | | | feasibility of switching from longitudinal to |
| a computer system in that all the information that is | | | | perpendicular recording techniques. The advantage is |
| permanently stored is contained within its enclosure, | | | | clearly one of capacity: when longitudinal magnetic |
| including your computer's Operating System (OS). | | | | particles are packed together, they take up much |
| Thanks to Hard Disk Drives, long gone are the days | | | | more space than if they were to stand upright, if |
| when you would have had to keep all your programs | | | | they stood perpendicular to the platter. More than |
| and documents stored on removable media such as | | | | merely a matter of initial capacity gain, perpendicular |
| Floppy Disks or CD-ROMs. | | | | recording technology avoids a problem which has |
| Originally invented in the mid 1950's and made | | | | been well known in the field for many years: the |
| commercially available in 1956 by International | | | | super-paramagnetic effect (SPE), which affects |
| Business Machines (IBM). Called RAMAC (Random | | | | magnetically charged particles of such small size as |
| Access Method of Accounting and Control), the first | | | | that used in Hard Disk Drives. "The |
| Hard Disk Drives contained as much as 50 platters | | | | super-paramagnetic effect is a phenomenon |
| which were 24 inches in diameter and were | | | | observed in very fine particles, where the energy |
| computers in their own right albeit with a single | | | | required to change the direction of the magnetic |
| purpose - to store data. The entire unit which housed | | | | moment of a particle is comparable to the ambient |
| the hard drive was the approximate size of two | | | | thermal energy" (source: Wikipedia.org).Many theories |
| large refrigerators placed side by side. In the 50 or so | | | | have cropped up over the years as to what density |
| years since their invention, Hard Disk Drives have | | | | magnetic particles (described by a disks areal density) |
| steadily and aggressively far out paced Moore's law. | | | | may achieve before becoming subject to SPE. At |
| Which stipulates that memory in computers will | | | | present it is suggested that anything from 100Gbit |
| increase by 100% approximately every 18 months. | | | | inch2 to 150Gbit/inch2 is the physical limitation for |
| Hard Disk Drives on the other hand have increased | | | | longitudinal Hard Disk Drives, although perpendicular |
| capacity in the same period by approximately 130%, | | | | media solutions have been made as high as 230Gbit |
| an increase of 100% every nine months in many | | | | inch2. |
| cases. Such capacity increases are being threatened, | | | | In the layering of the magnetic particulates atop a |
| however. In the years since the first Hard Disk Drive | | | | magnetic suspension layer and orienting the particles |
| very little has changed apart from logical steps in | | | | perpendicular to the platter, the recording medium |
| technology such as the increased speed or improved | | | | can pack many more magnetically sensitive particles |
| interfaces, the basic technology has changed very | | | | together in the same space than previously possible |
| little. There have been no technological leaps, as it | | | | whilst keeping SPE at bay. Perpendicular recording |
| were, for Hard Disk Drives beyond their increased | | | | technology does not however preclude SPE from |
| miniaturisation. Apart from miniaturisation and | | | | limiting capacity in the future, more than anything |
| recording media improvements the Hard Disk Drive as | | | | perpendicular recording technology can been |
| a device is almost identical technologically speaking, to | | | | described as a way to give manufacturers breathing |
| the very first, the RAMAC.Hard Disk Drives use a | | | | room to develop more permanent technological |
| similar technology as is employed in audio and video | | | | solutions such as holographic lithography or a |
| cassettes. Such audio and video cassettes use a | | | | multilayered recording medium. Traditional recording |
| magnetic ribbon wound around a two wheels to | | | | media manufacture consists of the spreading of |
| store data. To access a particular portion of the data | | | | recording material over a disk platter via a centrifugal |
| contained on the magnetic ribbon, the device must | | | | force induced by spinning the platter whilst the |
| wind the tape such that the beginning of the section | | | | recording material is placed atop its surface. The |
| containing the data is underneath the device that | | | | centrifugal force would spread the recording material |
| reads the data (the magnetic read/write head). This | | | | across the surface, evenly spreading it in all directions. |
| process is called sequential data retrieval because in | | | | Perpendicular recording media manufacture on the |
| the process of accessing the particular data, the | | | | other hand requires a much different technique. |
| device must sequentially read each piece of data until | | | | The exact manufacturing process of perpendicular |
| the data it's looking for is found. This process is very | | | | recording media is unsurprisingly a closely guarded |
| time consuming and contributes to wear. | | | | secret, especially considering its recent arrival on the |
| Hard Disks on the other hand use a circular | | | | marketplace. From patents filed at the United States |
| disk-shaped platter upon which the magnetically | | | | Patent and Trademark Office (USPTO), it can be |
| sensitive compound is laid. Such platters are similar in | | | | taken that the predominant technique involves the |
| concept to a Compact Disk (CD) in that the data | | | | laminating of magnetic and non-magnetically charged |
| they hold can be accessed randomly, that the | | | | metals such as chromium, cobalt, platinum and alloys |
| recordable media is in a circular (disk) shape, and that | | | | of similar; sandwiching unique layers to affect the |
| the data is sectioned off into tracks and sectors. | | | | desired result - a recording medium such that the |
| Data on a Hard Disk Drive can be accessed randomly | | | | magnetic particles are aligned perpendicular to the |
| because the recordable medium of Hard Disk Drives | | | | platter. In US patent number 6387483, filed by the |
| uses these separated tracks and sectors. By | | | | NEC Corporation of Tokyo; it describes the technique |
| separating the data in such a way, it can be | | | | as follows:The perpendicular magnetic recording |
| positioned at random intervals of the disk, depending | | | | medium of the embodiment is formed by laminating a |
| upon the space requirements. | | | | Cr film, a soft magnetic under layer film, and a |
| Anywhere from one to seven recordable platters are | | | | perpendicular magnetizing film on a substrate in this |
| contained within a modern Hard Disk Drive's metallic | | | | order. (Source: USPTO no. 6387483) |
| enclosure. Hard Disk Drive platters are perfectly | | | | In longitudinal media manufacture too, laminating |
| circular disks made from either an aluminium alloy or a | | | | multiple supportive metals is achieved; in perpendicular |
| more recently a glass ceramic substrate which is a | | | | media however, the difference is the magnetizing film |
| ceramic disk suspended in a glass outer shell. Onto | | | | as described above. Whereas traditional lamination |
| the surfaces of a disk's platter is laid a thin layer of a | | | | ordinarily serves only to prevent wear and noise |
| magnetically sensitive coating called the recording | | | | (both electro-mechanical and audible noise), in |
| medium, in modern drives the mixture is a complex | | | | perpendicular media manufacture it would appear that |
| amalgam of different materials such as cobalt | | | | at least some of the lamination process is used to |
| chromium platinum boron (CoCrPtB) and other such | | | | magnetize the magnetic media particles to a |
| rare metals. | | | | perpendicular orientation. Precisely how the |
| How does a Hard Disk Drive store data? | | | | reorientation of magnetic media particulate is |
| All information located on a computer is expressed as | | | | accomplished is not easy to determine, most |
| a series of ones and zeros (1/0), as binary digits | | | | probably because the technology is so new that such |
| (bits). Taking advantage of the nature of magnetic | | | | details are sketchy at best and obscure or guarded |
| particles, that they can be polarised to magnetic | | | | at worst. This fact is not at all surprising concerning a |
| north or south and that their magnetic poles can be | | | | new technology such as perpendicular magnetic |
| alternated or switched when a sufficient magnetic | | | | media development. |
| field of the correct polarity is applied, Hard Disk | | | | The future of storage technology |
| Drives can store the very same sequence of bits | | | | Perpendicular magnetic media technology as discussed |
| onto a disk by polarising the required magnetic | | | | earlier is merely a temporary solution, to find more |
| particles on the recording medium such that they | | | | permanent solutions we must look to much more |
| represent the data being stored. Hard Disk Drives are | | | | advanced technologies. One such technology is |
| sectioned off such that they contain both | | | | patterned magnetic media. The process of patterned |
| intersecting tracks and sectors. The purpose of | | | | magnetic media aims to make singular magnetic |
| which is to provide a logical data structure, to provide | | | | particulates the object of recording bits, you will |
| a way to distinguish between areas of data. Within | | | | remember that current technologies requires |
| each track there are a number of sectors. It is within | | | | approximately 500 to 1000 magnetic particles to |
| these sectors of the Hard Disk which data is stored. | | | | store a single bit. The object of patterned media is |
| The platter of a Hard Disk Drive is coated with a | | | | to cut this dramatically down to a single particle per |
| magnetically sensitive coating comprised primarily of | | | | bit. Advantages of such a technology are such as |
| magnetically charged particles or filings which as a | | | | reduced statistical noise associated with granular |
| whole may be called the recording medium. These | | | | media and more increased areal density (as much as |
| particulates can be magnetically aligned such that | | | | 64Gbit/inch2). |
| they represent binary digits, by inducing an | | | | Patterned magnetic media aims to prevent the SPE |
| electromagnetic field upon them via a devices read | | | | barrier, or at least further decrement its effect |
| write head. The recording media contains many billions | | | | through the use of so-called mesas and valleys. The |
| of microscopic particles which when viewed | | | | technique uses the creation of barriers between |
| extremely close resemble miniature metal filings. | | | | magnetic particles, thereby avoiding the SPE |
| When a Hard Disk Drive records data onto the | | | | complication which affects closely packed particles. |
| medium it takes many hundreds (usually anywhere | | | | Holographic Storage (a.k.a. Holographic Lithography) |
| from 500 to 100) of these magnetically sensitive | | | | too is a technology that aims to increase storage |
| particles to store a single binary digit. The increased | | | | capacity which is also under heavy research, and |
| reduction of the amount of particles required to | | | | claims to be a much more permanent solution. Unlike |
| record data is highly limited by the precision of the | | | | Patterned Magnetic Media, Holographic Storage is a |
| read/write head (the miniature device that reads and | | | | revolutionary step away from magnetic media and |
| records data onto the recording medium) because | | | | previous optoelectronic technologies. |
| the magnetic field which is used by the drive's read | | | | Hard Disk Drives will always be subject to inertia and |
| write head to read and/or record (write) data is such | | | | centrifugal force induced by the moving parts of the |
| that it already tentatively borders nearby data. | | | | drives mechanical components (platter, read/write |
| Should it be shrunk much further in an attempt to | | | | head), Holographic Storage has no such issues; the |
| increase precision, the likelihood of data corruption | | | | holographic process uses lasers in replacement of the |
| would increase vastly. Research by various parties | | | | read/write head of a Hard Disk Drive and the media |
| has been on-going to find a workable solution to | | | | itself requires no momentum (unlike the platters in |
| recording data onto much fewer or even single | | | | Hard Disk Drives). |
| particles for some time now. A hard drive may | | | | Such holographic storage is far from realisation, in |
| record data onto the Hard Disk Drive by applying a | | | | fact it is postulated by some that it may be as much |
| sufficient magnetic field to the section of the | | | | as ten years before the technology can be made |
| recording medium (which is suspended upon the Hard | | | | into a workable solution. In direct symmetry to early |
| Disks platter) such that the data (a series of ones | | | | memory research, research on Holographic Storage |
| and/or zeros which correspond to the information | | | | technologies seems to have banded into two camps: |
| being stored) is recorded onto the medium by aligning | | | | one of super fast data retrieval and extraordinarily |
| the specified particles to the desired magnetic pole | | | | high capacity storage; no doubt there will be |
| (north or south). In doing so, any previous data which | | | | extremely profitable markets for both. |
| was present is therefore destroyed. | | | | |