Ferrite Apertured Plate for Random-Access Memory

Abstract

Plates with an array of apertures molded from rectangular loop ferrite can be used for random access memory. With the relatively close center-to-center spacing equal to twice the hole diameter there is negligible interaction between adjacent holes. The nonconductive ferrite plate can be coated with a conductive pattern to form a winding linking all holes in series. The plates can be stacked and the whole stack threaded with word address selecting wires. The printed windings serve for reading and writing the digits of the word. An experimental prototype plate was developed. It has 256 holes of 0.025 inch in a square 0.830×0.830 inch. A current of 330 ma reverses the magnetization around a hole in 1.5 ?sec and produces 30 mv. The hysteresis loop has good rectangularity and the properties of the holes are uniform within ± 5 per cent. The memory plates can be driven by a switch, itself made of plates. Several novel switching principles are proposed: switching over all holes of a switch-row but the selected one, using memory plates in pairs, and operating by a flux-limited fashion. This results in read-out signals free of disturbs, fast access, and large operating tolerances. Conventional current coincident operation is possible also. The making, testing, and assembling of ferrite memory plates with printed windings requires much less time and labor than corresponding techniques with conventional cores. The plates open possibility of random access memories with capacities of millions of bits.