Data processor system with high storage capacity and program security - has central processing unit programme store selection protected by gated control signals

The data processing system is designed so that with microprocessors and microcomputers with with limited storage capacity, over-written programmes and/or several different programmes can be accommodated. A number of ROM type programme storage modules are provided which are individually selected via the central processor. The selection signals are only operational if certain signals not due to the user, occur in coincidence so that unauthorised reading-out of the data stored in the programme modules is prevented. The selection signals are coupled with different control signals via logic gates. The selection signals from the central processor can be stored in a store change-over unit so that the central processor needs to supply a selection signal only when the user programme is changed.