As we pack more and more logic elements into smaller and smaller volumes and clock them at higher and higher frequencies, we dissipate more and more heat.
Portable systems exhaust their batteries.
When a computational system erases a bit of information, it must dissipate ln 2 x kT energy , where k is Boltzmann's constant and T is the temperature. This is roughly the kinetic energy of a single air molecule at room temperature. This erasure is done very inefficiently, and much more than kT is dissipated for each bit erased. If we are to continue the revolution in computer hardware performance we must continue to reduce the energy dissipated by each logic operation. Today, because we are dissipating much more than kT , we can do this by improving conventional methods, i.e., by improving the efficiency with which we erase information.