Controlling a computer like the CSC-2 is conceptually the same as the CSC-1 with the addition of needing to specify a 3-bit A address, a 3-bit B address and a 3-bit C address at all times. Since there are 8 registers, we need log₂8=3 bits in the addresses. In some cases, we may not want to store back a value into any register, such as when we store the value in the MBR into memory. In these cases, the scratch register TMP may be specified, or the pseudo-register +1, since it cannot be modified.