Today data storage is dominated by the use of magnetic disks. Storage densities of about more than 5 Gb/cmhave been achieved. In the past 40 years areal density has increased by 6 orders of magnitude. But there is a physical limit. It has been predicted that superparamagnetic effects- the bit size at which stored information become volatile as a function of time- will limit the densities of current longitudinal recording media to about 15.5 Gb/cm2.In the near future century nanometer scale will presumably pervade the field of data storage. In magnetic storage used today, there is no clear-cut way to achieve the nanometer scale in all three dimensions. So new techniques like holographic memory and probe based data storage are emerging. If an emerging technology is to be considered as a serious candidate to replace an existing technology, it should offer long-term perspectives. Any new technology with better areal density than today's magnetic storage should have long-term potential for further scaling, desirably down to nanometer or even atomic scale.
The only available tool known today that is simple and yet offer these long-term perspectives is a nanometer-sharp tip like in atomic force microscope (AFM) and scanning tunneling microscope (STM). The simple tip is a very reliable tool that concentrates on one functionality: the ultimate local confinement of interaction. In local probe based data storage we have a cantilever that has a very small tip at its end. Small indentations are made in a polymer medium laid over a silicon substrate. These indentations serve as data storage locations. A single AFM operates best on the microsecond time scale. Conventional magnetic storage, however, operates at best on the nanosecond time scale, making it clear that AFM data rates have to be improved by at least three orders of magnitude to be competitive with current and future magnetic recording. The "millipede" concept is a new approach for storing data at high speed and with an ultrahigh density.
Millipede is a nano-storage prototype developed by IBM that can store data at a density of a trillion bits per square inch: 20 times more than any currently available magnetic storage medium. The prototype's capacity would enable the storage of 25 DVDs or 25 million pages of text on a postage-stamp sized surface, and could enable 10 gigabytes (GB) of storage capacity on a cell phone. Millipede uses thousands of tiny sharp points (hence the name) to punch holes into a thin plastic film. Each of the 10-nanometer holes represents a single bit. The pattern of indentations is a digitized version of the data. According to IBM, Millipede can be thought of as a nanotechnology version of the punch card data processing technology developed in the late 19th century. However, there are significant differences: Millipede is rewritable, and it may eventually enable storage of over 1.5 GB of data in a space no larger than a single hole in the punch card. Storage devices based on IBM's technology can be made with existing manufacturing techniques, so they will not be expensive to make. According to Peter Vettiger, head of the Millipede project, "There is not a single step in fabrication that needs to be invented." Vettiger predicts that a nano-storage device based on IBM's technology could be available as early as 2009.