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Researchers create superefficient 'inexact' chip

Posted: 18 May 2012     Print Version  Bookmark and Share

Keywords:computer chip  microchips  pruning technology 

A group of researchers have showcased what they claim as a super-efficient "inexact" computer chip that "challenges the industry's 50-year pursuit of accuracy."

"In terms of speed, energy consumption and size, inexact computer chips like this prototype, are about 15 times more efficient than today's microchips," the researchers claim.

The research, which earned best-paper honours at the 'ACM International Conference on Computing Frontiers' in Italy, was led by Indian-origin scientists Krishna Palem, who serves as director of the Rice-NTU Institute for Sustainable and Applied Infodynamics (ISAID).

According to Palem, the design improves power and resource efficiency by allowing for occasional errors. "It is exciting to see this technology in a working chip that we can measure and validate for the first time," he stated. "Our work since 2003 showed that significant gains were possible, and I am delighted that these working chips have met and even exceeded our expectations."

The concept is deceptively simple: Slash power use by allowing processing components—like hardware for adding and multiplying numbers—to make just a few mistakes, Palem noted. By managing the probability of errors and limiting which calculations produce errors, the designers claim they can simultaneously cut energy demands while dramatically boosting performance.

One example of the inexact design approach is "pruning," or trimming away some of the rarely used portions of digital circuits on a microchip. Another innovation, "confined voltage scaling," trades some performance gains by taking advantage of improvements in processing speed to further cut power 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, the team delved deeper and implemented their ideas in the processing elements on a prototype silicon chip."

"In the latest tests, we demonstrated that pruning could cut energy demands 3.5 times with chips that deviated from the correct value by an average of 0.25 per cent," said study co-author Avinash Lingamneni, a Rice graduate student. "When we factored in size and speed gains, these chips were 7.5 times more efficient than regular chips. Chips that got wrong answers with a larger deviation of about 8 per cent were up to 15 times more efficient."

Project co-investigator Christian Enz of Switzerland's Centre for Electronics and Microtechnology (CSEM) added, "Particular types of applications can tolerate quite a bit of error. For example, the human eye has a built-in mechanism for error correction. We used inexact adders to process images and found that relative errors up to 0.54 per cent were almost indiscernible, and relative errors as high as 7.5 per cent still produced discernible images."

Initial applications for the pruning technology is expected to be in application-specific processors, such as special-purpose "embedded" microchips like those used in hearing aids, cameras and other electronic devices.

It is to be noted that the inexact hardware is also a key component of ISAID's 'I-slate' educational tablet, which is designed for Indian classrooms with no electricity and too few teachers.

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.

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