Posted on 10/11/2002 1:50:47 PM PDT by Ernest_at_the_Beach
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The storage capacity of computer hard drives could skyrocket if a prototype device for magnetic data storage developed by IBM can be commercialized. The new system, unveiled by Manfred Albrecht and colleagues at the IBM Almaden Research Center in San Jose, California, could offer 200 times the data storage capacity of current state-of-the-art systems, such as IBM's Microdrive. The Microdrive, announced in 2000, is a magnetic disk the size of a small coin. It can store a billion bytes of data - a gigabyte - on two square centimetres of surface. It can hold a up to 1,000 books 200 pages long, or 18 hours of music. The patterned perpendicular magnetic film devised by Albrecht and colleagues crams in an extraordinary 200 gigabytes per square inch1. This leaps off the scale of the steadily increasing trend in hard-drive storage density of over the past couple of decades. But the new system is still far from the marketplace: it would require changing the hardware involved in recording data on a magnetic disk. Flip side Information is stored in magnetic tape and disks using magnetic 'write' and 'read' heads. These alter or detect the direction of the magnetic field in a thin film coating the storage medium. If this field points one way, it is equivalent to a '1' in the binary code used for digital data; in the opposite direction, the field denotes a '0'. Each bit of data - each 1 or 0 - is stored in a small patch of the magnetic film. The storage density is limited by how small these patches can be. In conventional magnetic tape or disks, the magnetic field is parallel to the surface of the film: it lies flat, pointing either one way or the other. If the patches are too small they can be spontaneously flipped by the magnetic fields of their oppositely aligned neighbours, erasing the data. Magnetizing the thin-film recording medium perpendicular to the film surface instead does away with this limitation. It makes oppositely aligned patches stable and resistant to flipping. But there is then another lower limit to the size of patches: if they become too small, heat in the surroundings can destroy the magnetization. An iron bar magnet becomes non-magnetic only when heated above 770 °C, but very tiny magnetic domains can be disrupted even at room temperature. Isolating such domains can protect them. In other words, instead of writing data into tiny patches in a continuous magnetic film, it would be written into discrete islands of magnetic material. Albrecht and colleagues have taken a step in this direction. Pattern power The IBM team have made films of a magnetic alloy of cobalt, chromium and platinum. With a finely focused beam of ions they cut the films into rows of square magnetic islands each just 26 millionths of a millimetre across. This corresponds to a storage density of 206 gigabytes per square inch. Writing data into these rows and reading it back out again is not straightforward, however. Current write and read heads are much bigger than the individual islands. This isn't a problem if the rows are well separated because the head would see only one row at a time - this is how the researchers demonstrated the principle of storing one bit per island. But the islands would have to be packed close together to achieve the full improvement in storage density. So smaller heads will ultimately be needed. And if the data are to be stored on a pre-imposed magnetic grid of islands, the electrical pulses used for writing have to be synchronized correctly as the write head moves over the grid. This synchronization is possible in IBM's prototype system - but making it widely available would require another big change in existing hard-drive technology. |
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