A COATING of microscopic polystyrene beads can dramatically increase the memory capacity of hard discs, as well as cutting the time a computer takes to access the data.

Since the early 1990s, the capacity of hard discs has doubled roughly every 18 months. The computer industry faces constant pressure to pack ever more data onto hard discs, for example, to support better graphics for games, or to store a library of digital movies. But the pace is beginning to ease. "The slowdown has been coming for a few years," says James Porter, an industry analyst and founder of Disk Trend in Mountain View, California.

Now Manfred Albrecht from the University of Konstanz in Germany and colleagues from the Hitachi San Jose Research Center in California have come up with a novel way to increase the amount of data discs can store.

All personal computers and network servers contain magnetic hard ...