HARD disks dominate the field of computer memory. They store oodles of information—which is why they are so useful. But they are also slow, heavy and power-hungry. Unfortunately solid-state memories, such as flash, that do not have these disadvantages are too expensive for stashing the vast programs needed to run a modern computer. What engineers would like is a device that combines the best of both. And a group of them have now taken a step towards developing such a piece of kit—a magnetic memory with no moving mechanical parts.

The idea began a few years ago when Stuart Parkin, who works at IBM's Almaden Research Centre in San Jose, California, worked out how to use a wire to store information magnetically. It has now been improved by Guido Meier, of the University of Hamburg. As he reports in Physical Review Letters, Dr Meier has taken Dr Parkin's idea and speeded it up to the point where it might eventually make a practical technology for computer users.

Traditional hard drives employ electrodes called heads to create tiny magnetic regions, known as domains, on the surface of a plate as it spins. The alignment of the north and south poles of each domain indicates whether it represents a one or a zero of the binary code—and that alignment can be read by a second head. Dr Parkin's wire is also divided into domains. But instead of moving the wire to bring those domains under the heads, in the way that a spinning hard disk would, his device moves the domains themselves along the wire, using an electric current. A wall between two domains represents a “one”; the absence of wall in a place where one might be expected represents a “zero”.

Magnetism is, ultimately, the result of a quantum-mechanical property known as spin. In particular, every electron has its own magnetic field aligned with the axis of its spin. If the electrons are spinning at random, these fields cancel each other out. If they are aligned, they reinforce each other to create a field that can be detected from the outside.

Both research groups use wire made of a standard alloy of nickel and iron that is easy to magnetise. They create domains along the length of the wire, in which the spins of the electrons of the atoms in the wire are aligned. Then they run pulses of current through the wire.

When a current flows in such a wire, the electrons that flow as electricity are forced to align their spins to those of the local atoms embedded in the wire. This means that when they come to a boundary between two different domains, their spins flip. That flip transfers angular momentum to the domain wall, pushing it along in the direction of the current. By using short and intense bursts of current, a succession of domain walls can be shoved past a reading head. It works like a tape, except that there are no moving spools.

The biggest problem with getting such an idea off the laboratory benchtop and onto the factory floor is the speed at which the domain walls travel. Until now, this has been a hundredth of the velocity that theory predicted. Which is where Dr Meier comes in. He and his colleagues (and also Dr Parkin, in a separate experiment) have persuaded practice to match theory. They report speeds of 110 metres a second, comfortably competitive with the speed of a hard disk. Their trick was to shorten the lengths of the pulses of current to about a nanosecond. Rapidly changing currents exert a greater force on domain walls than do slowly changing ones.

For the technology to work like a disk, though, the same bits of data will have to pass repeatedly under the reading and writing heads. That means the wires will have to loop. Dr Parkin is now working on integrating the technology with traditional silicon chips by inserting the ends of the wires into a chip to form U–shaped loops reminiscent of an ancient Roman hippodrome. Indeed, he refers to the technology as a magnetic racetrack. Time to place your bets?