The noise problem in the coincident-current memory matrix

Abstract

Magnetic ferrites which have square hysteresis loops are being used as memory elements in high-speed digital computers. The limiting factor in memory reliability is the noise generated by the magnetic cores which are subjected to field excitations of amplitude insufficient to cause a reversal of magnetization. The occurrence of such excitations (half-amplitude pulses) at any given core in almost any possible sequence is inherent in the two-to-one coincident-current method of register selection. The noise voltage induced by a magnetic core when excited by a half-amplitude pulse can be expressed through an equation listed in the document. The region of validity of the equation is discussed with reference to particular ferrite materials. The incremental permeability is shown to depend both on the direction (relative to the remanent state) of the applied pulse and on the sequence of excitation since the most recent magnetization reversal. The contributions from rotation, domain-wall motion, and reverse-domain nucleation and the mechanism responsible for the permeability difference are discussed. Also data are presented on the dependence of the various noise voltages on the amplitude and waveform of the pulse excitations. The meaning of these data with regard to the noise problem is discussed.