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Magnetic data recording beyond limits

diciembre 29, 2019

It was 1956 when IBM presented the world premiere of "RAMAC": the first 24-inch hard drive capable of recording 2,000 bits on a surface of one square inch. Since then, "bits" have passed under the bridges. Between 1956 and 1991 the surface density increased at a rate of 23%: a doubling of capacity every three years. In the following six years, the average annual increase in surface density increased by up to 61%, making a leap forward predicted by few. In fact, the capacity of magnetic media doubled every year and a half. Only three years ago it was believed that magnetic technology was very close to reaching its limits and, in this perspective, many hard disk companies began to diversify by investing in research and development in optical technology. Observing the past years, we notice that from 1997 to today the capacity of magnetic supports has continued in its crazy run, doubling every 10/12 months. Today on a 3.5-inch disk on the market they record 14.3 Gbit per square inch, which means a recording density of 7.15 million times higher than that of the first hard disk in history. With this recording density, it is possible to store 20 Gigabytes of information on the two surfaces of a single 3.5-inch magnetic disk.

The superparamagnetic limitIn the field of information technology, not even the most promising one of semiconductors (on the basis of which the famous microprocessors are built), stands comparison. According to Moore's law, transistors wired on increasingly infinitesimal computer chips double the frequency every 18 months. It was believed that at the beginning of the new millennium the physical limits of technology would be reached: "the superparamagnetic limit". According to this limitation "the size of a recorded bit would reach a point where, theoretically, it is no longer stable" (definition found in the US book "Magnetic Recording, the first 100 years"). This means that each magnetic particle that retains a charge must be large enough and sufficiently isolated so as not to interact with the adjacent particle. This limit which seemed to be near now, however still far from being reached. The leading companies in this market are bitterly competing for it by investing hyperbolic figures in the further development of this technology. In a race against time, the leaders push their technology to bring more capable, faster and quieter hard drives to the market before others, although these new services are often not required by the market. If only a few years ago the 20 GB per plate seemed like a dream, today we can say with certainty that the 300 GB per plate are within our reach.

The word to the laboratoriesThe tech announcement war began in late 1999 with the news that a consortium of Read Rite, HMT, and Marvell Semiconductor companies had achieved a recording density of 36 Gigabit per square inch in the lab. A little later, in March 2000, Seagate regained leadership, demonstrating in its labs that it has reached 45 Gigabit per square inch. This surprising result was possible using a GMR (Giant Magneto Resistive) reading head and an inductive writing head, both mounted on a small head holder arm (pico-slider). Together with these, thanks to a photolithographic process capable of reducing the size of a trace to one third of a micrometer, it was possible to reach an exceptional density of 70,000 traces per inch.The resonance of this announcement had not yet ceased to produce its echoes, when in April 2000, TDK and NEC reveal that prototypes of new TMR (Tunnel Magnetio Resistive) heads developed in their laboratories are able to improve the signal / noise ratio of the GMR heads. Thanks to TMR heads it is possible to reach 50 Gigabits per square inch. The entry into production of this new technology scheduled for 2002. Only a few weeks later the leadership changed hands again. Three companies, Komag, Read Rite and Marwell announce that they have achieved 50.2 Gigabits per square inch by adopting traditional GMR cartridges and a density of 90,900 tracks per inch. In addition to the increased density of traces per inch, the surprising result obtained thanks to a thermally stable magnetic support with low coercivity. A representative of Read Rite says, for the occasion, that the same technology will allow to reach 80 to 100 Gigabits per square inch. The twists and ends do not end there. Hitachi reports that it has developed, together with the Japanese MITI (Ministry of International Trade and Industry), a technology capable of recording 52.5 Gigabit per square inch. The only technological detail revealed shakes the consolidated foundations of technology: it is vertical registration, and not longitudinal as tradition would have it. This is a road hypothesized in the past but never proven until that moment. According to Hitachi, this technology can easily reach 80/100 Gigabit per square inch. Just a few days later, Japanese IT giant Fujitsu announces LEXIS (Layer EXchange Interaction Stabilized): a technology that has proven to be able to 56 Gigabit per square inch. Fujitsu worked on the problem of overheating (thermal degradation), which makes the stored information unstable until loss can be determined, and which represented the main limitation to the development of high density storage technology. The Fujitsu development team has been able to reduce the effects of the phenomenon of thermal degradation of information by inserting a protective layer under the surface on which the data is recorded. This new protective layer does not limit the reading of the information but, magnetically approaching the recording surface (anti-ferromagnetic coupling), it stabilizes it by preserving the stored signals from degradation. This technology combined with the new TMR heads, according to Fujitsu, can achieve a recording density of 300 Gigabit per square inch. Leaving the field of demonstrable realities, IBM introduces us to the most ethereal world of pure research, stating that new materials chemicals with innovative magnetic properties, will allow to produce hard drives with a capacity of 100 times higher than the current ones. This means that the perspectives indicated by IBM, although still to be demonstrated, indicate that it is possible to achieve recording densities of 1,750 Gigabit per square inch.

We do not live on IT aloneA technology that seemed to have come to an end therefore still has many "tricks up its sleeve" to play not only in the traditional computer sector, but also in the broader and more widespread markets for consumer equipment. In two or three years we will see hard drives growing so much in capacity and performance that it is possible to record high definition movies in real time. This will change the way we will watch television allowing us to watch only the broadcasts we like (pay per view), when we want (video on demand) and with the ability to access the film sequence from anywhere instantly. Increasingly smaller and more capable hard drives will find their place in digital cameras, satellite navigation systems, video recording systems and in all fields where great storage capacity, immediate access, and data transfer speed are required. In order to achieve these objectives, complementary technologies are needed to reduce consumption, increase resistance to vibrations and shocks and reduce noise. Many of these technologies are already in an advanced state of development and it is already possible today to purchase hard disks whose sound emissions are difficult to perceive by the human ear.

Where are the limits?Currently we can only say that a limit to the development of magnetic technology certainly exists, but no one yet able to see how far it extends and what the impassable boundary is. We certainly know that many years of unexpected surprises and applications are unlikely to await us The open battle, the well-known players, the battlefield ideally located in the Pacific ocean between Japan and the United States, the weapons made up of colossal investments in Research & Development and increasingly nourished groups of researchers / scientists. beautiful.

(Edited by Newton)

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