This article has a speed-of-light theme, we may as well talk about it. > How far do you think light travels in one nanosecond given the optimal conditions? In

This article has a speed-of-light theme, we may as well talk about it. > How far do you think light travels in one nanosecond given the optimal conditions? In one nanosecond, the light travels only about 30 centimeters. This means that if you want something computed in under 1 nanosecond, the signal starting your computation has to go through all the transistors that do the computation by the path that is only 30 centimeters in length. In real circuits, light travels in a medium, not in free space or air. The speed-of-light in a medium depends on its relative dielectric constant K of the insulator material. For standard SiO2, it's approximately 4, giving a speed of 0.5c, or only 15 centimeters per nanosecond (coincidentally, a typical circuit board has roughly the same dielectric constant, even coax, CAT-6, or fiber optics cables are not far off from it, 15 cm/s is an useful number to remember). In the history of process node improvements, various doping techniques have been developed for decreasing (or increasing) the K for better performance. The primary motivation of lowering the K is not increasing the speed-of-light, but to reduce parasitic capacitance, charging and discharging a capacitor creates a much longer delay than the theoretical propagation delay of c / sqrt(K). https://en.wikipedia.org/wiki/Low-%CE%BA_dielectric https://en.wikipedia.org/wiki/Low-%CE%BA_dielectric Another area of research is optical interconnects. https://en.wikipedia.org/wiki/Optical_interconnect https://en.wikipedia.org/wiki/Optical_interconnect