Stackable storage. It's the ultimate space saver, making order out of chaotic cabinets, closets, attics and garages. But until recently it had not made its way into the realm of computers, where megabytes of data are scattered on the face of a disk like millions of shoes across a bedroom floor. Now a few big-name media makers, including Lucent Technologies and IBM, are making important strides in developing optical holography, which stacks information throughout the thickness of a storage medium, instead of just writing it to the surface.

Holographic storage relies mainly on laser light and a photosensitive material-usually a crystal or a polymer-to save data. It works by splitting a laser beam in two. One beam contains the data and is referred to as the "object beam"; the other holds the location of the data and is known as the "reference beam." The two beams intersect to create an intricate pattern of light and dark bands. A replica of this so-called interference pattern gets engraved three-dimensionally into the photosensitive material and becomes the hologram. To retrieve the stored data, the reference beam is shone into the hologram, which refracts the light to replicate the data beam.

The holographic technique packs data so tightly that one 12-centimeter disk could eventually hold a terabyte of data-about as much information as 200 DVDs. What's more, holographic storage opens the possibility of reading and writing data a million bits at a time, instead of one by one as with magnetic storage. That means you could duplicate an entire DVD movie in mere seconds.

The idea of storing tons of data three-dimensionally was first proposed by Polaroid scientist Pieter J. van Heerden in the 1960s. But developing the technology was difficult, because the required optical equipment was large and expensive. A typical laser back then, for example, was two meters long. Today, lasers are measured in mere centimeters and are much cheaper.