Perpendicular recording: Why it matters

Hard-drive capacity is running up against physical limits, says Hitachi Global Storage CEO Jun Naruse, but an old technology may save the day.

5 min read
While the hard-drive industry has been using longitudinal recording successfully for five decades, it is now within two product generations of reaching its practical limit.

For about the past decade, scientists and engineers have pondered the potential effects of a natural phenomenon called superparamagnetism and postulated when its presence might interfere with the progress of the hard-disk drive, or HDD, industry.

Since the first commercial hard drive was introduced, in 1956, the industry has grown storage capacity exponentially by decreasing the size of the magnetic grains that make up data bits. In effect, the smaller the magnetic grain, the smaller the bit, the more data that can be stored on a disk. With longitudinal recording, we are getting close to the point where data integrity will be harmed if we continue to shrink the magnetic grains. This is due to the superparamagnetic effect.

Superparamagnetism occurs when the microscopic magnetic grains on the disk become so tiny that random thermal vibrations at room temperature cause them to lose their ability to hold their magnetic orientations. What results are "flipped bits"?-bits whose magnetic north and south poles suddenly and spontaneously reverse?-that corrupt data, rendering it and the storage device unreliable.

Today, the hard-drive industry?s ability to push out the superparamagnetic limit is more critical than ever as capacity requirements continue to grow dramatically. This is due, in large part, to the increasing use of hard drives in consumer electronic devices and the desire to pack more and more storage capacity on smaller devices. The superparamagnetic effect on current magnetic recording technologies will make that growth impossible within one-to-two years.

The superparamagnetic barrier is drawing nearer, forcing the industry to slow the historically rapid pace of growth in disk drive capacity.

Thanks to renewed interest in a magnetic recording method first demonstrated more than 100 years ago, there's confidence in the storage industry that the natural effects of superparamagnetism can be further stalled. That method is called perpendicular recording, which, when fully realized over the next five-to-seven years, is expected to enable a tenfold increase in storage capacity over today's technology. This would, for example, enable production of a 60GB 1-inch microdrive--a higher-capacity version of the microdrives used in MP3 players, personal media players, digital cameras, PDAs and other handheld devices.

To help understand how perpendicular recording works, think of the bits as small bar magnets.

In conventional longitudinal recording, the magnets representing the bits are lined up end-to-end along circular tracks in the plane of the disk. If you consider the highest-density bit pattern of alternating 1s and 0s, then the adjacent magnets end up head-to-head (north pole-to-north pole) and tail-to-tail (south pole-to-south pole). In this scenario, they want to repel each other, making them unstable against thermal fluctuations.

In perpendicular recording, the tiny magnets are standing up and down. Adjacent alternating bits stand with north pole next to south pole; thus, they want to attract each other, are more stable and can be

packed more closely. This is the key to making the bits smaller without superparamagnetism causing them to lose their memory.

Earlier this year, Hitachi demonstrated a perpendicular recording-data density of 230 Gigabits per square inch?-twice that of today's density on longitudinal recording--which by 2007 could result in a 20GB microdrive.

Though it departs from the current method of recording, perpendicular recording is technically the closest alternative to longitudinal recording, enabling the industry to capitalize on current knowledge while delaying the superparamagnetic effect.

The superparamagnetic barrier is drawing nearer, forcing the industry to slow the historically rapid pace of growth in disk drive capacity-?a pace that, at its peak over the past decade, doubled capacity every 12 months. Using perpendicular recording, the effects of superparamagnetism can be further forestalled, which would create opportunities for continued growth in real density at a rate of about 40 percent each year.

Perpendicular magnetic recording represents an important opportunity for companies in the hard drive industry to continue to grow capacities at a reasonable pace. Such growth is needed to satisfy the burgeoning information requirements of society: A 2003 University of California at Berkeley study estimates that more than 4 million terabytes of information were produced and stored magnetically in 2002?-more than double the 1.7 million terabytes produced and stored in 2000. There are no signs that the requirements for hard-disk storage is ebbing.

Industry analysts have predicted that hard drives for consumer electronics will account for 40 percent of all hard drive shipments by 2008, up from 9 percent in 2003 and 15 percent in 2004. More than ever, consumers are holding their entertainment and personal data in digital formats and have demonstrated an insatiable appetite for storing music, photos, videos and other personal documents. In the next five to 10 years, the average household will have 10 to 20 hard drives in various applications--a situation that will require the successful adoption of perpendicular recording. Companies that research and produce their own hard drive technologies will be better positioned to do this when the industry demands it.

Confidence for the future
Fifty years ago, when the first 5MB drive was introduced, few if any observers could have predicted the current state of the industry. They would likely not have believed that a read/write head could fly 100mph over a spinning platter at a distance that is less than 1/10,000th the width of a human hair. Or that hard drives the size of matchbooks would be capable of storing entire music libraries. This all would have been in the realm of science fiction.

Yet they would likely understand the scientific concepts and physical laws that have made these advances possible. While there has been a great deal of invention, the basic science--like Danish inventor Valdemar Poulsen's discovery of magnetic recording more than 100 years ago--has remained relatively constant.

Such constancy gives rise to confidence across the industry that the challenge of superparamagnetism will be met. Perpendicular recording is most likely the first technology bridge in this realm, but it is by no means the last.