pixie dust or antiferromagnetically-coupled (AFC) media

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 (basically, alterations in magnetic orientation). 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 (gigabyte) hard drives for desktop computers, and 200 GB hard drives for laptops by 2003.

In information technology, the term "pixie dust" is often used to refer to a technology that seemingly does the impossible. 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. Hard drive capacities have more or less doubled in each of the last five years, and it was assumed in the storage industry that the upper limit would soon be reached. The superparamagnetic effect has long been predicted to appear when densities reached 20 to 40 gigabits per square inch - close to the data density of current products. AFC increases possible data density, so that capacity is increased without using either more disks or more heads to read the data. Current hard drives can store 20 gigabits of data per square inch. IBM began shipping Travelstar hard drives in May 2001 that are capable of storing 25.7 gigabits per square inch. Drives shipped later in the year are expected to be capable of 33% greater density. Because smaller drives will be able to store more data and use less power, the new technology may also lead to smaller and quieter devices.

IBM discovered a means of adding AFC to their standard production methods so that the increased capacity costs little or nothing. The company, which plans to implement the process across their entire line of products, chose not to publicize the technology in advance. Many companies have focused research on the use of AFC in hard drives; a number of vendors, such as Seagate Technology and Fujitsu, are expected to follow IBM's lead.

This was last updated in September 2005

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