Computers: Magnetic disks: Storage densities on the rise: New materials and new techniques, such as vertical and magnetooptical recording, are driving down costs per stored bit

For 30 years, magnetic-disk memories have been the mainstay of computer information storage, and the information density of the disks has steadily increased to 2 million bits per centimeter squared. But the demand for ever greater packing densities has not slackened. As a result, a number of companies are today pushing for higher disk densities along four main fronts.