The wires coming from registers are labeled by their register's name followed by OUT. Thus, A-OUT, S-OUT, MBR-OUT. The memory has a set of 16 wires which it uses to send data to the MBR register. These are labeled MEM-OUT. All these OUT wires can be referred to individually by number: A-OUT0, S-OUT14, and MEM-OUT3. All registers except MAR are 16 bits wide, so their outputs are labeled 0 to 15. The MAR has 12 bits.