Summarized from an article by Jon William Toigo in Scientific American, May 2000

Computers get better and better, faster and faster; and, of all computer components, probably the greatest rate of evolution belongs to the stalwart hard drive. On a daily basis, the storage capacity and speed of hard drives increases, while their cost just keeps on shrinking. This is one of those rare situations in which both consumers and companies profit; but something called superparamagnetic effect may soon bring an end to this golden age.

As hard drives become capable of storing more information and accessing it at faster speeds, their data becomes more susceptible to corruption. This data-density barrier is known as the superparamagnetic effect (or SPE). Before going on to say more about SPE, though, it might be helpful (and scenic) to take a brief detour to examine the technology at the hub of your average hard drive.

Today's hard drive resembles a small record player that's capable of stacking its disks, or platters, to hold up to eight of them at a time. Each platter is covered with a magnetic film that is ingrained with tiny particles called bits. When a read-write head (looking like the needle of a record player) passes over the bits, it either magnetically aligns the particles to record information (turning them into series of 1's and 0's), or it reads them in order to access previously-stored data. These operations take place at phenomenal speeds; the platters spin around thousands of times per minute, and both sides of them are scanned simultaneously by read-write heads.

Advances in hard drive technology continue to increase the number of bits that fit onto each platter. Bits are getting smaller and smaller, making for greater storage capacity, but also bring the SPE barrier closer and closer. So what exactly does SPE do? Basically, SPE destabilizes the 0 or 1-orientation of magnetic bits, resulting in corruption of stored data. When the energy in the bits' atoms approaches the thermal energy around them, the bits start randomly switching between 0's and 1's. In layman's terms, SPE makes bits flip out.