Special ferrite cores for NDRO memories

New square-loop ferrite toroids were developed especially for NDRO memories with permeability sensing. They are 20-mil cores (outer diameter) with a coercive current of 80 mA. The information 0 is written by a short but high set pulse of uncritical amplitude (about 1000 mA). To write the information 1 in a selected address, the concerning core must be demagnetized in a coincident current mode. Applying a read pulse with an amplitude of 50 mA and a rise time of 5 ns results in a peak voltage for a single core of about 2.5 mV in the 0 state and about 7 mV in the 1 state. In a plane a two-core-per-bit system will be used so that bipolar sense signals appear.