Ferrite-core stores are at present the most suitable high-speed memory system for use in a parallel digital computer. The relevant properties of ferrite memory cores and the way in which they are interconnected and interrogated in a coincident-current core store are reviewed, and some specific limitations are considered.The paper is based on an experimental investigation into the noise voltages which can appear on the sense wire of a coincident-current memory plane using ferrite cores. There are two largely independent types of asymmetry which can occur in a cancelling pair: (a) the information held may be different and (b) the final half-current disturbances may have been in opposite senses. The ‘worst noise’ condition arises when (a) and (b) are present together in such a way that their effects add. Means by which this pattern can occur in a practical memory are discussed, and waveforms are presented to illustrate the phenomena. A ‘post-write-disturb’ pulse, staggered read currents and a split sense wire can reduce the noise by ten to one. A rectangular sense-wire threading can largely eliminate the shock-excited decaying oscillations produced by stray couplings.