The world's smallest hard drive stores four gigabytes on a disk the size of a postage stamp. That's the capacity of about 4 CD-ROMs on a one-inch square. Hitachi plans to release it this fall.

The device is called a Microdrive, the latest in a line of tiny drives originally sold by IBM. The new model is intended to replace traditional flash memory in gizmos like handheld computers and MP3 players. A user could insert it into a digital camera and take dozens or even hundreds of snapshots.

The new Microdrive is so small that its read-write head is about the size of a grain of salt. It can scan the dense disk, which holds over 60 billion bits of data per square inch. "The Microdrive enables users to focus on the task at hand-not on the amount of memory available in their device," boasted Hitachi General Manager Bill Healy.

The Microdrive is the tiniest in an onslaught of tiny disks for portable storage. Some tiny storage cards hold hundreds of megabytes and fit on a key chain-or are even worn as jewelry. They aim for an increasingly mobile, increasingly high-tech population.

As storage increases, people can have more computing power without being tethered to a desktop PC. This technology is becoming like electrical power and running water, part of the warp and woof of ordinary life.