The Junkyard Powerhouse
------------------------------------------------------------------ This article first appeared in Forbes Magazine in September, 1998. ------------------------------------------------------------------
BUNCH OF DUTCH engineering students interning at Hewlett-Packard's Palo Alto laboratories in 1995 wanted to translate magnetic resonance imaging data into a three-dimensional map of the brain's arteries. HP gave them a refrigerator-size gizmo made of junk parts-processor chips with high defect rates. The experimental machine, called a Teramac, ran 100 times faster than a top-end workstation, and the students went home thrilled. What is this Teramac? Tera means "trillion," signifying the designers' intention that the machine perform a trillion operations per second. It is the first computer purposely made out of junk-processor and memory chips that "any sane engineer would refuse to ship," in the words of Philip Kuekes, 51, who helped to design it. The software detects any hardware flaws and simply steps around them. Meet a manufacturing idea that may supplant a concept at the very heart of modern life: the concept that parts should be so precisely formed that they become interchangeable. "We're proposing to do the exact opposite," says Kuekes. "Get rid of mechanical precision and use computer power to make up for the imprecision." In the Teramac, quantity substitutes for quality. There is precedent for the Teramac approach-in the peripherals business. Since flawless disk drives are costly, it is cheaper to supply highly reliable mainframe storage via arrays of inexpensive redundant disks. If each file is stored in duplicate on multiple disks, and if the multiple copies are carefully compared whenever the file is retrieved, the data can be made as close to error-free as you want. It helps that small disk drives of the sort that go into consumer products are getting dirt cheap. The same kind of economics surfaces in the chip business. Quantity is easy to come by: As Moore's Law dictates, the transistor count on chips is already in the millions and will someday reach into the billions. But quality is costly. Producing defect-free chips with ever more microscopic detail will demand factories costing tens of billions of dollars. One day it will cost too much to continue the process, and Moore's Law will slow to a crawl. Yet you could extend the Law's life quite a bit if you could teach computers to tolerate defects. HP got the defect-ridden behemoth to work by having software make up for the failings of hardware. First, the software spent a week of processing time to find, map and catalog the 220,000 defects that sullied the hardware. For most computers, a single one of those defects would have been fatal. Then the software set about rewiring the machine to get around the trouble spots. It had the means to do so because Teramac's chips, made by HP, came with extra logic elements (called "gates")-backup systems, as it were. "You could even clip wires or purposely break a part and then reconfigure the computer, and it would work fine," says James Heath, a UCLA chemistry professor who collaborated on Teramac. You might wonder how a machine built of defective parts could correctly test itself for defects in the first place. It turns out that 7% of its parts-the ones that diagnose and correct errors-do have to be perfect. So why not switch immediately to these self-fixing computers? Because it's not economical yet. Teramac relies on especially large chips, which use more silicon and are therefore expensive. For now, it's still cheaper to junk defective Pentiums when they come out of the factory, and use only the perfect ones. As a result, the Teramac architecture is most likely to find its first applications in niche markets that require bigger chips. One likely prospect: digital cameras, which need a large light-sensing chip to get a sharp picture. Other applications include special-purpose computing, as in a television set-top box or in medical electronic instruments. Because Teramac rewires itself readily, it can optimize its hardware, first for one task, then another. In other words, it can substitute hardware for software. Further down the road lies perhaps Teramac's most promising application, as an enabling technology for super-small circuitry. Such nanoelectronic devices, as they are called, still smack of science fiction, with parts that aren't etched but are self-assembled, almost like living things. The hoped-for result would be a workstation-standard computer smaller than a grain of sand. You could never guarantee the perfection of a trillion transistors that had been cooked up in this fashion. You'd need a computer architecture that could live with the defects. Says Heath, who first did work on nanocomputer components in 1992: "Teramac is very significant; we would have been wandering in the woods without it. We'd have continued making wiring and gates in beakers without knowing how to assemble them into a computer." First on the agenda is getting Teramac to pay for itself. If the cost of perfect parts rises fast enough, it will make sense to use a larger quantity of junkyard parts. It could happen in as little as five years, says Stanley Williams, a physical chemist who has used Teramac in his own research.