Hewlett-Packard Labs is attempting to catapult the memristor, the fourth passive circuit element after resistors, capacitors and inductors, into the electronics mainstream. Invented in 1971, this "memory resistor" represents a potential revolution in electronic-circuit theory akin to the invention of the transistor -- and perhaps its time has finally come. But as with that earlier device, it will take a killer application to get it off the ground.

Where the hearing aid played that role for the transistor, Hewlett-Packard Labs (Palo Alto, Calif.) hopes resistive random-access memories (RRAMs) will open the floodgates for the memristor. HP Labs is promising prototypes of these ultradense memory cells next year.

"I'd say memristors give HP a chance to become the dominant leader in memory technology in 10 years," said Martin Reynolds, vice president of Gartner Inc. (Stamford, Conn.). "We have seen HP reinvent itself a number of times in the past, and this is a technology that could really drive that kind of change in the company again."

However, the clock is ticking. Last year, HP's crossbar switches -- the building blocks of a new memory type the company is developing -- were more than 20 times denser than flash memories, giving HP breathing room to perfect its RRAMs. But in less than a year, flash memories have upped their density fourfold to eightfold by going to 2- and 3-bit-per-cell configurations, respectively.

That unforeseen leap has narrowed HP's advantage. RRAMs now claim just three times the density of flash, evoking memories of the same scenario that has doomed other next-generation memory technologies.

"When HP started work on the crossbar several years ago, they were 40 or 50 times denser than flash," said Reynolds. "But now they are only about three times denser than flash." To stay ahead, he said, HP will have to figure out how to boost the memristor's current density of 100 Gbits/cm2 "to a terabit in a square centimeter."