Abstract: A memory space for storing computer instructions includes first and second groups of addresses for first and second types of computer instructions. The first and second groups of addresses are numbers in first and second bases, respectively. The memory space is addressed with signals representing numbers only in the second base. All of the addresses of the first base are expressed by numbers that form only some of the numbers of the second base. In response to an indication of the first type of computer instruction being read out of or into the memory, the addresses of the first base are converted into addresses of the second base.