Pixie dust is the informal name that IBM is using for its antiferromagnetically-coupled (AFC) media technology, which can increase the data capacity of hard drives to up to four times the density possible with current drives. AFC overcomes limits of current hard drives caused by a phenomenon called the superparamagnet effect.
AFC allows more data to be packed onto a disk. The pixie dust used is a 3- atom thick magnetic coating composed of the element ruthenium sandwiched between two magnetic layers. The technology is expected to yield 400 GB hard drives for desktop computers, and 200 GB hard drives for laptops.
IBM s use of AFC for hard drives overcomes what was considered an insuperable problem for storage: the physical limit for data stored on hard drives. IBM discovered a means of adding AFC to their standard production methods so that the increased capacity costs little or nothing.