http://www.hinduonnet.com/fline/stories/20071102506412900.htm
Volume 24 - Issue 21 :: Oct. 20-Nov. 02, 2007
INDIA'S NATIONAL MAGAZINE
from the publishers of THE HINDU
Excerpts:
NOBEL PRIZE
A disk revolution
R. RAMACHANDRAN
Albert Fert and Peter Grünberg jointly win this year’s Nobel Prize in Physics for the discovery of giant magnetoresistance.
 | THE first computer hard disk drive (HDD) was introduced by IBM in 1956. Called the 305 RAMAC (Random Access Method of Accounting and Control), this first data storage system comprised 50 disks, each about 60 metres in diameter, and stored about five megabytes of information. This corresponded to a data density of a mere 200 bits per square centimetre. The density in today’s hard disks is touching a whopping 10 billion (or giga) bits per sq cm. That is a 50-million-fold increase in hard disk storage capacity in just 50 years, a rate much faster than the rate at which the number of components crammed into a silicon integrated circuit (IC) chip has grown in the same period (see graph). |
While the latter has determined the rapid growth in the speed of the computer processor, the former is an equally, if not more, important component of the ongoing information technology revolution. Ever-shrinking hard disks have not only led to slenderer and sleeker laptops and more powerful servers and search engines, they have also changed the very concept of personal entertainment, with the development of pocket-size devices such as the MP3 player and the iPod, which can store hours of music and images.
The empirical Moore’s Law, which states that the number of components on a chip doubles every 18 months and which the growth in processor technology has followed until now, is essentially governed by advances in the technology of packaging transistors into an IC. There have been attempts to describe the exponential growth in data storage capacity by a similar law, called Kryder’s Law, but it has not conformed to any simple relationship like Moore’s Law. This is because advances in HDD technology have been due to the constant interplay between progress in basic science – which is difficult to predict – and its quick application. This year’s Nobel Prize in Physics has been awarded for one such unexpected but fundamentally new discovery called giant magnetoresistance (GMR) that has revolutionised hard disk technology.
During 1988-89, Albert Fert of Paris-South University, Orsay, France, and Peter Grünberg of the Jülich Research Centre, Germany, who share the Nobel award, independently discovered the new physical effect of GMR, which refers to very weak magnetic changes giving rise to unexpectedly large changes in electric resistance in certain systems. Such a GMR system has proved to be the perfect device for retrieving densely packed digital data from hard disks and has provided the much-needed technological leap for read-out heads in the present generation of HDDs.
A better read-out capability implies that a greater amount of information can be packed in a hard disk. This immediately led to the development of smaller and thinner hard disks with increasing storage capacities, which have now found their way into the new pocket-size electronic wonders. That a new scientific discovery can get translated into industrial-scale technology in less than a decade is unique for any finding. IBM introduced the first 16.8-gigabyte GMR-based HDD in 1997. Describing this development, the IBM website says: “To some people, 10 years = a decade; to IBM research, 10 years = a revolution.”
After bubble memory devices and flash memory cards, the development of data storage devices seemed to have hit a technology wall. It was as if the rapidly advancing information-driven world was waiting for a breakthrough like GMR. It is the concurrent advances in related disciplines that made the immediate exploitation of the discovery possible. Indeed, HDD is only the first of the possible applications of GMR, and its impact is already enormous. But the effect holds immense promise for future technology developments in the field.
How does an HDD work? Understanding this will help one appreciate the significance of the discovery. Information in a hard disk is stored digitally in the form of tiny magnetised regions. Magnetisation in one direction could be taken to represent the binary digit “0” and that in another to the binary digit “1”. In modern HDDs, different elements of a single device write and read data as it flies over the spinning disk. The read-out head picks up the different fields of magnetisation as it scans the disk. As hard disks become smaller, each magnetised area, the bit, also correspondingly shrinks. In a tightly packed hard disk, the magnetic fields of individual bits, therefore, become weaker and require more and more sensitive read-out devices.