How can I get 8 bits output from 4 bit CPU?


I am very new to Computer architecture. I am thinking to add one more output register to this 4 bit CPU as shown below. However, I am not sure should I connect the output register to the current CPU. Should I connect it just the same way as the current one and label the 2 output register as output A and output B? But if I connect it the same way, the input data from ALU to output registers will always be only 4 bits, how should I get 8 bits output from the two output registers? enter image description here