On 9/20/2013 1:22 PM, Chris de Morsella wrote:
>> A computation always takes a nonzero amount of energy to perform, theoretically you can make the energy used be as close to zero as you like, but the less energy you use the slower the calculation. How does that square with the increased (well measured) energy efficiency per fundamental unit of logic (single machine operation) -- it takes far less energy to perform an elementary logic operation on a modern CPU than it did on say a CPU from ten years ago (even if the modern CPU may suck down more total power -- it is performing far more work) Modern CPUs clearly are also operating at much higher speeds. I think you are not factoring in the dimension of scale or the physical size of the logic container/state-machine. As the size of a logic gate is scaled down it takes less energy and can operate at a higher clock speed.
http://en.wikipedia.org/wiki/Performance_per_watt
"For example, the early UNIVAC I <http://en.wikipedia.org/wiki/UNIVAC_I> computer performed approximately 0.015 operations per watt-second (performing 1,905 operations per second (OPS), while consuming 125 kW). The Fujitsu <http://en.wikipedia.org/wiki/Fujitsu> FR-V <http://en.wikipedia.org/wiki/FR-V> VLIW <http://en.wikipedia.org/wiki/VLIW>/vector processor <http://en.wikipedia.org/wiki/Vector_processor> system on a chip <http://en.wikipedia.org/wiki/System_on_a_chip> in the 4 FR550 core variant released 2005 performs 51 Giga-OPS with 3 watts of power consumption resulting in 17 billion operations per watt-second.^[1] <http://en.wikipedia.org/wiki/Performance_per_watt#cite_note-1> ^[2] <http://en.wikipedia.org/wiki/Performance_per_watt#cite_note-2> This is an improvement by*over a trillion times in 54 years*."
Size (or rather the lack of it) matters in this equation.



But there still a limit because entropy has to be dumped into the environment, which is not at 0deg, if a register is to be erased.

http://en.wikipedia.org/wiki/Landauer%27s_principle

But we are many orders of magnitude from the Landauer limit now - lots of room for improvement.

Brent



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