Magnetic Film Memory Design

Thin magnetic films of permalloy have characteristics ideal for high-speed digital storage. A simple rotational model modified to include the effects of wall switching and dispersion of the preferred direction of magnetization provides a basis for describing properties of engineering interest. A selection system has been chosen which allows great latitude in film uniformity. Production of films with magnetic properties uniform to within ± 10 per cent is readily achieved. Specifications for operation in a destructive mode can easily be met by existing film arrays; the nondestructive mode is considerably more stringent unless very small signals can be tolerated. The first film memory has been in reliable operation since the summer of 1959. It has 32 ten-bit words and has been operated with a minimum cycle time of 0.4 , ¿sec. Higher speed and larger capacities will require higher bit densities and improved techniques to minimize undesirable coupling between drive and sense lines. The use of 10 × 60 mil rectangles, balanced sense windings, and longer words will hopefully permit memories of about 200,000 bits with cycle time under 0.2 ¿sec.