Patent US 4,095,281

Transistor memory cells which may be operated in both the erasable "read only" and the "random access" modes. Each cell includes a plurality of MOS transistors interconnected to permit random access storage and at least two MNOS transistors. The latter may be set, one to one threshold level and the other to a second threshold level to represent read only storage of a logic 1, and the threshold levels may be reversed to represent read only storage of a logic 0. The MOS transistors may be randomly accessed both for read and write independently of what the MNOS transistors are storing.