.B.M. scientists say they have created a data-storage technology that can store the equivalent of 200 CD-ROM's on a surface the size of a postage stamp.
Writing in the current issue of the journal IEEE Transactions on Nanotechnology, researchers at I.B.M.'s laboratories in Zurich report that they have achieved a storage density of one trillion bits of data per square inch, about 25 times as great as current hard disks.
Dr. James C. Ellenbogen, an expert on molecular electronics at the Mitre Corporation in McLean, Va., described the work as "incredible engineering."
Still more remarkable, this new technology is a return to an obsolete one, at least in concept. Like computer punch cards — which were invented more than a century ago and went out of vogue in the 1970's, about the same time as slide rules — I.B.M.'s system stores data in a pattern of little holes.
But I.B.M.'s holes are much, much tinier — half of a billionth of an inch across. While mechanical devices have steadily given way in recent decades to electronic ones that are faster, cheaper and more reliable, that trend may reverse at the molecular scale, where friction and wear and tear act differently.
"Back to the future of mechanics," said Dr. Peter Vettiger, leader of the I.B.M. project, known as Millipede. Millipede has another advantage over punch cards: the holes can be closed up so that data can be rewritten over and over.
Nantero, a start-up company in Woburn, Mass., is also taking a mechanical approach. Scientists there are making computer memory using nanotubes — rolled-up sheets of carbon graphite — that open and close like mechanical switches.
"It's counterintuitive because people assume in a computer-type application that if you have moving parts, it will be too slow and also it will break," said Greg Schmergel, president and chief executive of Nantero.
In electronic devices, data are stored in bundles of electrons, and as electronics shrink, the bundles contain fewer and fewer electrons. Smaller bundles of charge fall apart more easily.
Hard disks run into similar problems as storage densities rise. Instead of electrical charge, hard disks store data in what is essentially a vast array of tiny magnets. But if a magnet is shrunk too small, vibrations of heat can make the magnet flip, destroying data.
A hole, even one a few atoms wide, is a more resilient structure.
The Millipede project grew out of invention of the scanning tunneling microscope in 1981 by Dr. Gerd Binnig and Dr. Heinrich Rohrer at the I.B.M. Zurich laboratories. By measuring the current passing between a sharp microscopic silicon tip and a surface, the new microscope generated images of individual atoms. Dr. Binnig and Dr. Rohrer won the Nobel Prize in Physics in 1986.
Dr. Binnig said he realized early on that the silicon tip might be used to poke holes in a surface. "I certainly realized the method is usable for storage," he said.
Six years ago, Dr. Binnig and Dr. Vettiger started working on the Millipede project in earnest.
The Millipede chip consists of a layer of plexiglass a couple of billionths of an inch thick laid on a silicon chip. To write a bit of data, a microscope tip, heated to 750 degrees Fahrenheit, softens the plexiglass and dents it.
To read data, the tip is heated to 570 degrees — not hot enough to deform the plexiglass — and pulled across the surface. When it falls into a dent, the tip cools because more surface area is in contact with the cooler plexiglass. That temperature drop reduces its electrical resistance, which can be easily measured.
To erase data, a hot tip is passed over the dent, causing it to pop up.
In the latest work, the I.B.M. researchers show that they can now erase individual dents; previously, they had to erase large patches at once. They have also shown that they can reliably erase and rewrite data.
Millipede still suffers a big drawback of mechanical systems. Reading and writing data with a single silicon tip takes about 1,000 times as long as with hard disks.
To compensate, a second prototype chip uses 1,024 silicon tips to read and write data in parallel, bobbing up and down like a flock of birds pecking at dirt over a square area about a tenth of an inch wide.
The work is still years from becoming a commercial product, but it has progressed far enough that Dr. Binnig, 55, will retire from I.B.M. at year's end to spend more time on interests like painting and composing music. "It's in a state where all the big problems are solved," he said.
Last year, Dr. Charles M. Lieber, a professor of chemistry at Harvard, and Dr. Thomas Rueckes, a graduate student, reported that they had made computer memory out of nanotubes. Each bit of data is stored in two of nanotubes placed at right angles and separated by a small space. Applying a voltage to the tubes creates an electric field that pushes them together. Once stuck, the nanotubes remain held together by molecular forces even when the voltages are turned off. That means data would remain in memory when the computer was turned off.
Applying an opposite voltage separates the tubes.
After completing his doctorate, Dr. Rueckes, along with Mr. Schmergel, founded Nantero in October. They aim to produce a prototype by the end of next year and to go into production within a year after that.
They also think they could produce much higher densities than could be possible with conventional memory, where neighboring bundles of electrical charge interfere with one another if pushed too close.
With the nanotube memory, they need only to move the nanotube pairs closer to each other.
"Neighboring bits don't affect each other," Mr. Schmergel said. "It's just mechanical."
