‘Inexact’ Computer Chip 15 Times More Energy Efficient
The prototypes cut energy use by allowing processing components – like hardware for adding and multiplying numbers – to make a few mistakes.
By managing the probability of errors and limiting which calculations produce errors, the designers – from Rice University, Singaporeâ€™s Nanyang Technological University, Switzerlandâ€™s Center for Electronics and Microtechnology (CESM) and the University of California, Berkeley – say they can simultaneously cut energy demands and boost performance.
One example of the inexact design approach is â€śpruning,â€ť or trimming away some of the rarely used portions of digital circuits on a microchip. Another innovation, â€śconfined voltage scaling,â€ť takes advantage of improvements in processing speed to further cut energy demands.
In their initial simulated tests in 2011, the researchers showed that pruning some sections of traditionally designed microchips could boost performance in three ways: the pruned chips were twice as fast, used half as much energy and were half the size. In the new study, which earned best-paper honors at the ACM International Conference on Computing Frontiers in Cagliari, Italy this month, the team implemented their ideas in the processing elements on a prototype silicon chip.
Study co-author Avinash Lingamneni, a Rice graduate student, says the latest tests show pruning could cut energy demands 3.5 times with chips that allow for errors .25 percent of the time. After factoring in size and speed gains, these chips were 7.5 times more efficient than regular chips, Lingamneni said. Chips that got wrong answers with a larger deviationâ€”about 8 percentâ€”were up to 15 times more efficient, he said.
The human eye has a built-in mechanism for error correction, CSEMâ€™s Christian Enz, a project co-investigator, said. Researchers found relative errors up to .54 percent were almost indiscernible, and relative errors as high as 7.5 percent still produced discernible images.
Project leader Krishna Palem, who also serves as director of the Rice-NTU Institute for Sustainable and Applied Infodynamics (ISAID), said likely initial applications for the pruning technology will be in application-specific processors, such as special-purpose â€śembeddedâ€ť microchips, like those used in hearing aids, cameras and other electronic devices.
The inexact hardware is also a key component of ISAIDâ€™s I-slate educational tablet, designed for Indian classrooms with no electricity and too few teachers. Officials in Indiaâ€™s Mahabubnagar District announced plans in March to adopt 50,000 I-slates into middle and high school classrooms over the next three years, according to Rice.
The hardware and graphic content for the I-slate are being developed in tandem. Pruned chips are expected to cut power requirements in half and allow the I-slate to run on solar power from small panels similar to those used on handheld calculators. Palem said the first I-slates and prototype hearing aids to contain pruned chips are expected by 2013.
In March, news reports said that Intel had developed a chip that can run on minute amounts of power, idling at 280 millivolts at 3MHz and drawing 737 millivolts of power at 915MHz.
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