Bounds on Minimal Energy Spent on Computations

Heat is dissipated in consequence of computations and must be removed to the ambient. Landaulet´s ultimate limit is very low compared to energy spent by contemporary microprocessors to process one bit of data. Moreover the ultimate limit cannot be reached without sophisticated data coding whereas microprocessors process uncoded bits. In the article data processing by logic gates is considered from Information Theory point of view. A simple model of a logic gate based on additive white gaussian noise (AWGN) channel is proposed. As a result an analytical formula for practical value of the low limit on energy spent on processing one bit of data if uncoded data are processed is obtained. The practical limit is nearly 100 times greater than the ultimate limit and is practically insensitive to basic technological factors. Using Moore´s law is possible to approximate time when the practical limit is reached. After that time a new design paradigm will be needed - reliable systems will be assembled with unreliable gates.