Error tolerance : Why and how to use slightly defective digital systems *

We provide an overview of the notion of error tolerance and describe the context that motivated its development. We then present a summary of some of our case studies, which demonstrate the significant potential benefits of error tolerance. We present a summary of testing and design techniques that we have developed for error tolerant systems. Finally, we conclude by identifying shifts in paradigm required for wide exploitation of error tolerance. The notion of error tolerance is motivated by three important trends in information processing, namely changes in fabrication technology, changes in the mix of applications, and emergence of new paradigms of computation. Fabrication technology: As we get closer to what some call the " end of CMOS " , we see the emergence of highly unreliable and defect-prone technologies. This is accompanied by rapid development of new computing technologies such as bio, molecular, and quantum devices. Most of these new technologies are also extremely unreliable and defect-prone (e.g., see [12]). However, these new technologies also provide the ability to carry out massive numbers of computations in parallel and at speeds that far exceed those currently achieved by CMOS devices. Applications: Increasingly larger fractions of the total number of chips fabricated in any given year implement multi-media applications and process signals representing audio, speech, images, video and graphics. The outputs of such systems eventually become input signals to human users. There are several interesting aspects to the computational requirements for such systems. 1) The result of computation, i.e., the output data, is not measured in terms of being right or wrong, but rather on perceptual quality to its human users. For example, in the case of an image the perceptual quality may be defined in terms of absence of visible artifacts, clarity, color and intensity. In other words, the criterion is not correctness but whether the end product is acceptable to the human user. 2) Most such systems are by design lossy, in the sense that the outputs deviate from perfection due to sampling of input signals, conversion to digital, quantization, lossy encoding, decoding and conversion to analog signals. 3) Many such applications require parallel architectures as they are computationally intensive and have real-time performance constraints. Emerging paradigms of computation: Several new paradigms are emerging on how functions are computed and what requirements are placed on the " correctness " and " accuracy " of the results. With tongue in cheek, …