Computers: Higher densities for disk memories: Despite rumors of their impending demise, disk memories are alive and well, and with good reason

Ten years ago, disk memory technology was widely thought to be exhausted, with no promise of significant future increases in bit density, and bound to be obsoleted soon by the new semiconductor memories. Yet, disks have defied all efforts since then to dislodge them as the dominant computer mass-storage devices. Their bit density has increased several hundred times in the past decade — as fast a growth rate as the more publicized semiconductor memories of recent years — and it may increase almost as fast in the 1980s. However, disk technology today is indeed straining the limits of recording on particulate media — a coating of gamma type iron oxide — although the fundamental magnetic limits are still several orders of magnitude away. Further density increases require improvements in recording media, read/write heads, and encoding methods. Nevertheless, rigid disk memories will probably have at least 108 bits per square inch by the late 1980s. The increased density will be obtained by further exploiting thin-film read/write heads, and particulate (iron oxide) recording media. Thin-film media or perpendicular recording may trigger new density increases by the late 1980s or the mid 1990s, depending largely on marketing considerations.