The control unit decodes the instruction LOAD 3 to mean LOAD the value at memory location 3 into this place, the Accumulator. The accumulator is another special purpose register. It’s like a warehouse where data is temporarily stored while mathematical and logical operations are performed by this place ... the Arithmetic Logic Unit, it is the factory of the city, and uses data stored in the accumulator to process calculations. So now that the Control Unit has decoded the instruction, the decode stage is complete. The control unit can now tell the other components to execute the program instruction, and we’re into the execute stage of the cycle. The 3 in LOAD 3 is an address, so the control unit first updates the Memory Address Register ... then a signal is sent to retrieve the data stored at memory address 3 … before the data there is sent back to the Memory Data register ... And finally makes its way to the Accumulator. Where that number 13 is stored, bringing the execute stage to an end, and completing the first fetch-decode-execute cycle. The next cycle begins and the whole process proceeds in much the same way. The next instruction, SUB 4, is fetched by the control unit. Now if LOAD 3 means load whatever value is at location 3 in the memory, it follows that SUB 4 means to subtract whatever value is being held at location 4 in the memory. The value at location 4 is fetched and we can see it’s the number 8. It gets loaded into the arithmetic logic unit. Now the full instruction, to subtract 8 from 13, can be executed. That number 13 gets sent to the arithmetic logic unit, which does the required calculation, before the result, 5, is sent back and stored in the accumulator. Ending the execute stage, and completing the second fetch decode execute cycle.