a high density read only memory structure is arranged to have the decoders and selectors which are used to access the read only memory arrays in a layer which is above and / or below the read only memory array layers . note that by layer it is meant a substantially planar structure with some thickness in which the circuitry that makes up particular functionality resides . thus , the inefficient two - dimensional structure of the prior art is folded over to create a compact read only memory device with a three - dimensional structure . connection of the decoders to the rows is not limited to the ends of the rows , but instead may be made at any point along the rows . similarly , connection of the selectors to the columns is not limited to the ends of the columns , but instead may be made at any point along the columns . advantageously , additional circuitry is not required on the periphery of the memory array , so that a smaller overall memory device is achieved . in addition , in order to reduce cross talk when reading the memory array with a low impedance amplifier , the memory is addressed using a single active row , and , it is read only one column at a time .