Low temperature storage elements

The philosophy underlying the use of low temperature computer elements is discussed and the cryogenic aspect of the problem briefly reviewed. The most advanced low temperature storage element at the moment is the Crowe cell, in which a persistent current is set up around an aperture in a thin superconducting film, the direction of the current determining whether a 0 or 1 is stored. The switching time of these elements can be as short as 10 m¿sec, and the size is such that between 106 and 107 can be packed into a cubic foot. The main problem involved in the fabrication of a large memory is that of reproducibility. To exploit the high speed of the Crowe cell it may be necessary to perform the selection and logical operations in the low temperature cryostat. Modifications of Buck´s original ¿Cryotron¿ or avalanche breakdown in a semi conductor could conceivably be used for this purpose.