Across the country, University of Virginia computer scientist David Evans has taken this notion of cellular segregation one step further. Three years ago, he and his colleagues developed a program that shows how a software network might function if limited to the same rules governing cellular interaction. In other words, modules communicate not by direct electronic query but in a fashion modeled on the physics of chemical diffusion. Signals move outward in a slow-moving spherical field, delivering information in variable doses.

While significantly slower than standard electronic communications, this diffusion strategy has one sizable advantage: When healthy components fail, the "signal" remains, leaving a distributed memory of its position and function, a memory the overall network can use to replace the damaged component.

To demonstrate survivability, Evans and his colleagues have taken a cue from biological evolution and programmed the individual modules to build and maintain an arbitrary three-dimensional superstructure -- a sphere, for example. Once it is built, various modules are subjected to damaging data and flushed out of the system when they fail. The question then becomes whether the superstructure can rebuild the same shape with a fraction of its original components.

So far, Evans says, diffused signaling works like a charm: "We can survive damage to nearly all the cells as long as the structure is maintained through these types of interactions."

Building cartoon spheres might seem a little frivolous, but Evans says the experiment has solid business-world roots. A security specialist, he says it was the creativity of Internet hackers that forced him to consider a more creative approach to network defense.

"The attackers have really taken advantage of the interconnectedness of the Internet," he says. "Defenders haven't."

With self-healing software at the blastula stage of software evolution, it seems a bit premature to speak of full-scale autonomic computing. Even so, NASA, DARPA, IBM (which boasts a 3-year-old Autonomic Computing Division) and a growing number of research underwriters have taken an active interest in seeing what's next. Evans' sphere project is already supported by the National Science Foundation. This summer, Evans and university colleagues John Knight, Jack Davidson, Anh Nguyen-Tuong and Chenzi Wang will start a new project backed by DARPA's Self-Regenerative Systems program. "[We'll] study approaches to system security inspired by biological diversity," he says.

Whether that inspiration leads to outright mimicry remains to be seen. For the moment, says IBM's White, terms like "self-healing software" and "autonomic computing" offer a convenient reference point for scientists eager to explore the next level of software complexity. Just as the sound barrier forced aircraft designers to radically revise aircraft and engine designs, so today's complexity barrier is forcing computer scientists to rethink systems design or, at the very least, to seek out new sources of inspiration.

"Today's systems have too many dials to watch; people can spend their whole lives figuring out how to make a database run well," White says. "We want to stand this notion of systems management on its head. The system has to be able to set itself up. It has to optimize itself. It has to repair itself, and if something goes wrong, it has to know how to respond to external threats. If I can think about the system at that level, I'm using humans for what they're good at, and I'm using the machines for what they're good at. That's the idea here."

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