Abstract: Computer instructions are stored in a main memory in encrypted or coded form, e.g., to conserve memory space. The coded instructions are decoded prior to execution. A temporary memory is provided to store, preferably, the last N decoded instructions. When an interrupt occurs and a refetch operation is required, a controller retrieves the desired instruction from the temporary memory already in decoded form. Thus, it only need be decoded once although used multiple times. The temporary memory can be much smaller than the main memory. Processing speed is enhanced while still conserving main memory space by coded instructions.