A computing technology based on superconductivity and electron tunnelling between metals. These effects usually occur at extremely low temperatures, obtained by immersing the whole system in liquid helium or liquid nitrogen. Logic circuits and nonvolatile memories can be made out of the technology, which has the potential for ultrafast switching speeds and very low power dissipation (see Josephson junction). This combination of properties offers the potential of extremely fast computers that can be realized within minimum linear dimensions and that do not have the heat transfer problems of VLSI silicon devices. As switching speeds become measured in picoseconds, system linear dimensions must be reduced accordingly. (One nanosecond is the order of 10 cm on a transmission line.)