The Junkyard Powerhouse

This article first appeared in Forbes Magazine in September, 1998.

By Dolly Setton

 		   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.